CN118050684A

CN118050684A - Frequency modulation continuous wave generator, working method thereof and millimeter wave radar system

Info

Publication number: CN118050684A
Application number: CN202311392787.6A
Authority: CN
Inventors: 林水洋; 宋颖; 崔科技
Original assignee: Gekong Microelectronics Shenzhen Co ltd
Current assignee: Gekong Microelectronics Shenzhen Co ltd
Priority date: 2023-10-25
Filing date: 2023-10-25
Publication date: 2024-05-17

Abstract

The invention provides a frequency modulation continuous wave generator, a working method thereof and a millimeter wave radar system, wherein the frequency modulation continuous wave generator comprises a first modulation module, a second modulation module, a combining module, an oscillator module and a signal processing module; the first modulation module modulates the received frequency modulation continuous wave signal based on the frequency modulation code word to obtain a first modulation voltage, the second modulation module performs digital-to-analog conversion on the received voltage modulation code word to obtain a second modulation voltage, the combining module combines the first modulation voltage and the second modulation voltage based on the first combining coefficient and the second combining coefficient to obtain a final modulation voltage, the oscillator module obtains the frequency modulation continuous wave signal based on the final modulation voltage, and the signal processing module is used for providing the frequency modulation code word and the voltage modulation code word. The invention solves the problem of poor performance of the traditional frequency modulation continuous wave generator in the aspects of frequency modulation range, frequency modulation slope, phase noise and the like.

Description

Frequency modulation continuous wave generator, working method thereof and millimeter wave radar system

Technical Field

The invention relates to the technical field of integrated circuit design, in particular to a frequency modulation continuous wave generator, a working method thereof and a millimeter wave radar system.

Background

Currently, millimeter wave radar chips applied to the consumer radar field and the automotive radar field are receiving more and more attention. Millimeter wave radar chips have become an indispensable key component in the consumer field, the auxiliary/automatic driving field because of their high accuracy, long distance, good angular resolution and weather interference free advantages.

In general, signals of millimeter wave radar chips are generated by a frequency modulation continuous wave generator (FMCW-PLL), and how to improve the frequency modulation range, frequency modulation slope, phase noise, and other performances of the FMCW-PLL is a technical problem that those skilled in the art want to solve.

Disclosure of Invention

In view of the above-mentioned drawbacks of the prior art, an object of the present invention is to provide a frequency modulation continuous wave generator, a working method thereof, and a millimeter wave radar system, which are used for solving the problem that the performance of the existing frequency modulation continuous wave generator is poor in terms of frequency modulation range, frequency modulation slope, phase noise, etc.

To achieve the above and other related objects, the present invention provides a frequency modulated continuous wave generator comprising:

The device comprises a first modulation module, a second modulation module, a combining module, an oscillator module and a signal processing module, wherein:

The first modulation module modulates the received frequency modulation continuous wave signal based on the frequency modulation code word to obtain a first modulation voltage;

the second modulation module performs digital-to-analog conversion on the received voltage modulation code word to obtain a second modulation voltage;

The combining module is connected with the output ends of the first modulation module and the second modulation module, and combines the first modulation voltage and the second modulation voltage based on a first combining coefficient and a second combining coefficient to obtain a final modulation voltage;

The oscillator module is connected with the output end of the combining module, and the frequency modulation continuous wave signal is obtained based on the final modulation voltage;

the signal processing module is configured to provide the frequency modulation codeword and the voltage modulation codeword.

Optionally, the frequency modulation continuous wave generator further comprises: the sampling module is connected between the combining module and the signal processing module, samples the final modulation voltage through analog-to-digital conversion to obtain a sampling code word, and the signal processing module obtains the voltage modulation code word based on the sampling code word.

Optionally, the first modulation module includes: sigma-delta modulator, multi-mode frequency divider, phase frequency detector, charge pump and loop filter;

The sigma-delta modulator obtains a frequency division codeword which changes with time based on the frequency modulation codeword;

The multi-mode frequency divider is connected with the sigma-delta modulator and the output end of the oscillator module, performs frequency division ratio setting based on the frequency division code word, and performs frequency division on the frequency modulation continuous wave signal according to the frequency division ratio to obtain a frequency division signal;

The frequency and phase discriminator is connected with the output end of the multi-mode frequency divider and is used for performing frequency and phase discrimination on the reference signal and the frequency division signal to obtain two paths of control signals;

The charge pump is connected with the output end of the phase frequency detector, and charge or discharge control is carried out based on two paths of control signals to obtain charge/discharge current;

the loop filter is connected with the output end of the charge pump and is used for converting the charge/discharge current into the first modulation voltage and performing high-frequency filtering.

Optionally, the second modulation module includes: the digital-to-analog converter performs digital-to-analog conversion on the voltage modulation code word, and then obtains the second modulation voltage through the modulation filter.

Optionally, the combining module includes a coefficient-adjustable adder.

Optionally, the oscillator module comprises a single variable capacitance voltage controlled oscillator.

The invention also provides a millimeter wave radar system comprising the frequency modulated continuous wave generator as described above.

The invention also provides a working method of the frequency modulation continuous wave generator, which comprises a normal mode, wherein:

modulating the frequency modulation continuous wave signal based on the frequency modulation code word to obtain a first modulation voltage;

Performing digital-to-analog conversion on the voltage modulation code word to obtain a second modulation voltage;

Setting a first combining coefficient and a second combining coefficient, wherein both the first combining coefficient and the second combining coefficient are larger than zero, and combining the first modulation voltage and the second modulation voltage based on the first combining coefficient and the second combining coefficient to obtain a final modulation voltage;

Obtaining the frequency modulation continuous wave signal based on the final modulation voltage;

Wherein, the voltage modulation code word corresponds to the frequency modulation code word one by one.

Optionally, the working method further comprises a calibration mode, wherein:

The first combining coefficient and the second combining coefficient are regulated, so that the first combining coefficient in a calibration mode is larger than or equal to the first combining coefficient in a normal mode, and the second combining coefficient is zero;

Sweep frequency is carried out based on the frequency modulation code word, and the final modulation voltage formed by the first modulation voltage is sampled through analog-to-digital conversion, wherein the frequency modulation curve slope corresponding to the frequency modulation code word in a calibration mode is smaller than or equal to the frequency modulation curve slope corresponding to the frequency modulation code word in a normal mode;

And taking a digital code corresponding to the difference voltage between the final modulation voltage and the sweep initial voltage as the voltage modulation code word, establishing a corresponding relation between the frequency modulation code word and the voltage modulation code word, and storing the corresponding relation.

Optionally, the first combining coefficient in the normal mode is 0.2, and the second combining coefficient is 1; the first combining coefficient in the calibration mode is 1.

As described above, the frequency modulation continuous wave generator, the working method thereof and the millimeter wave radar system of the invention realize the implementation of two-point modulation on the oscillator module with single variable capacitance by combining the first modulation voltage and the second modulation voltage by the design of the first modulation module, the second modulation module, the combining module, the oscillator module, the signal processing module and the sampling module; in the calibration mode, the control voltage of the oscillator module (namely the final modulation voltage formed by the first modulation voltage) is sampled based on an analog-to-digital conversion mode, a digital code corresponding to the difference voltage of the sweep initial voltage is used as a voltage modulation code word, the corresponding relation between the frequency modulation code word and the voltage modulation code word is obtained, and in the normal mode, the voltage modulation code word corresponding to the frequency modulation code word is output to the second modulation module to reproduce the difference voltage, so that the calibration of the single variable capacitor in the oscillator module is realized.

Drawings

Fig. 1 shows a schematic structure of a frequency modulated continuous wave generator.

Fig. 2 is a schematic diagram showing the fm transfer function of the fm continuous wave generator shown in fig. 1.

Fig. 3 shows a schematic structure of another frequency modulated continuous wave generator.

Fig. 4 is a schematic diagram showing the fm transfer function of the second modulation branch of the fm continuous wave generator shown in fig. 3.

Fig. 5 is a schematic diagram showing a frequency modulation transfer function of the frequency modulated continuous wave generator shown in fig. 3 after two modulation branches are superimposed.

Fig. 6 shows a schematic structure of the frequency modulated continuous wave generator of the present invention.

FIG. 7 is a schematic diagram showing signals associated with the FM continuous wave generator shown in FIG. 6 in a calibration mode.

Fig. 8 is a schematic diagram showing signals associated with the fm continuous wave generator of fig. 6 in a normal mode.

Fig. 9 is a schematic diagram showing the structure of the millimeter wave radar system of the present invention.

Description of element reference numerals

100. 200, 300 Frequency modulation continuous wave generator

101. 201 Digital signal processor

310. First modulation module

102. 202, 311 Sigma-delta modulator

103. 203, 312 Multi-mode frequency divider

104. 204, 313 Phase frequency detector

105. 205, 314 Charge pump

106. 206, 315 Loop filter

107. 207 Voltage controlled oscillator

320. Second modulation module

208. 321 Digital-to-analog converter

209. 322 Modulation filter

210. Counter

330. Combiner module

340. Oscillator module

350. Signal processing module

360. Sampling module

400. Millimeter wave radar chip

Detailed Description

Other advantages and effects of the present invention will become apparent to those skilled in the art from the following disclosure, which describes the embodiments of the present invention with reference to specific examples. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention.

Please refer to fig. 1 to 9. It should be noted that, the illustrations provided in the present embodiment merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings rather than the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complex.

Fig. 1 shows a circuit structure of a frequency modulated continuous wave generator 100, which includes a digital signal processor 101, a sigma-delta modulator 102, a multi-mode frequency divider 103, a phase frequency detector 104, a charge pump 105, a loop filter 106, and a voltage controlled oscillator 107, wherein the multi-mode frequency divider 103, the phase frequency detector 104, the charge pump 105, the loop filter 106, and the voltage controlled oscillator 107 form a phase locked loop, and the voltage controlled oscillator 107 is a voltage controlled oscillator with a single variable capacitance.

The digital signal processor 101 is configured to provide a frequency modulation codeword, the sigma-delta modulator 102 obtains a frequency division codeword that varies with time based on the frequency modulation codeword, the multi-modulus frequency divider 103 performs frequency division ratio setting based on the frequency division codeword and frequency division on the frequency division continuous wave signal according to the frequency division ratio to obtain a frequency division signal, the phase frequency discriminator 104 performs phase frequency discrimination on the reference signal and the frequency division signal to obtain two paths of control signals, the charge pump 105 performs charge or discharge control based on the two paths of control signals to obtain charge/discharge current, the loop filter 106 converts the charge/discharge current into a modulation voltage and performs high-frequency filtering, and the voltage-controlled oscillator 107 obtains the frequency modulation continuous wave signal based on the modulation voltage.

The circuit structure comprises:

Open loop transfer function Wherein K _PD is the tuning gain of the phase frequency detector 104 and the charge pump 105, K _VCO is the tuning gain of the voltage controlled oscillator 107, s is the complex variable operator of the rah transform, R ₁ is the resistance of the resistor R1 in the loop filter 106, C ₁ is the capacitance of the capacitor C1 in the loop filter 106, C ₂ is the capacitance of the capacitor C2 in the loop filter 106, and N is the frequency division ratio of the multi-modulus divider 103.

Closed loop transfer function of frequency modulated codeword to output frequency of voltage controlled oscillator 107Wherein ω _ref is the angular frequency of the reference signal.

At dc (i.e., when the value of the frequency modulated codeword is statically configured, the output frequency is multiplied by ω _ref, the output frequency reflects the change in the divide ratio), the transfer function H _CL1,dc＝ω_ref of the circuit structure.

To ensure loop stability, loop filter 106 is generally configured as C ₁>>C₂, and therefore, the approximate pole-zero of the closed loop transfer function described above can be obtained as follows:

ω_z＝ω_p1＜ω_p2＜ω_p3。

Wherein ω _p1 is a first pole angular frequency, ω _p2 is a second pole angular frequency, ω _p3 is a third pole angular frequency, ω _z is a zero angular frequency; the frequency modulation transfer function of the circuit structure is shown in fig. 2, and has low-pass characteristic, and the corner frequency is close to omega _p2.

For the frequency modulated continuous wave generator 100 shown in fig. 1, the frequency modulation slope is completely dependent on the loop bandwidth, and in order to improve the frequency modulation slope, a large loop bandwidth is required, which will cause deterioration of phase noise; in addition, in order to cover a large frequency tuning range, the tuning gain K _VCO of the vco 107 is usually large, which makes it necessary for the loop filter 106 to use a large area capacitor (generally referred to as capacitor C1) to maintain the required loop bandwidth, which increases the cost.

Fig. 2 shows another circuit configuration of a fm continuous wave generator 200, which includes a digital signal processor 201, a sigma-delta modulator 202, a multi-modulus divider 203, a phase frequency detector 204, a charge pump 205, a loop filter 206, a voltage controlled oscillator 207, a digital-to-analog converter 208, a modulation filter 209, and a counter 210, where the voltage controlled oscillator 207 is a voltage controlled oscillator with two sets of variable capacitors. The sigma-delta modulator 202, the multi-modulus divider 203, the phase frequency detector 204, the charge pump 205 and the loop filter 206 form a first modulation branch, the digital-to-analog converter 208 and the modulation filter 209 form a second modulation branch, and the two modulation branches respectively drive a set of variable capacitors in the voltage-controlled oscillator 207 to obtain a frequency modulated continuous wave signal.

The digital signal processor 201 is configured to provide a frequency modulation codeword and a voltage modulation codeword, the sigma-delta modulator 202 obtains a frequency division codeword that varies with time based on the frequency modulation codeword, the multi-modulus divider 203 sets a frequency division ratio based on the frequency division codeword and divides a frequency-modulated continuous wave signal according to the frequency division ratio to obtain a frequency division signal, the phase frequency discriminator 204 performs phase frequency discrimination on the reference signal and the frequency division signal to obtain two paths of control signals, the charge pump 205 performs charge or discharge control based on the two paths of control signals to obtain a charge/discharge current, the loop filter 206 converts the charge/discharge current into a first modulation voltage and performs high-frequency filtering, the digital-to-analog converter 208 performs digital conversion on the voltage modulation codeword to obtain a second modulation voltage via the modulation filter 209, the first modulation voltage and the second modulation voltage respectively control a set of variable capacitors in the voltage-controlled oscillator 207 to obtain a frequency-modulated continuous wave signal, the counter 210 samples the frequency-modulated continuous wave signal and performs frequency calibration via the digital signal processor 201 to obtain the voltage modulation codeword, and the frequency calibration accuracy depends on the count time of the counter 210.

The circuit structure comprises:

the analysis of the first path of modulation branch is the same as the circuit structure shown in fig. 1, and will not be described here again, where the first path of modulation branch has a low-pass characteristic.

Closed loop transfer function of voltage modulated codeword of second path modulation branch to output frequency of voltage controlled oscillator 207Wherein H _OL is an open loop transfer function of the first path modulation branch (see above), K _VCO2 is a tuning gain of the variable capacitor corresponding to the second path modulation branch, C is a conversion gain of the frequency modulation codeword to the voltage modulation codeword, s is a complex variable operator of the rah transform, N is a division ratio of the multi-modulus divider 203, R ₁ is a resistance value of the resistor R1 in the loop filter 206, C ₁ is a capacitance value of the capacitor C1 in the loop filter 206, C ₂ is a capacitance value of the capacitor C2 in the loop filter 206, K _PD is a tuning gain of the phase frequency detector 204 and the charge pump 205, and K _VCO is a tuning gain of the variable capacitor corresponding to the first path modulation branch (see above).

Also, due to C ₁>>C₂, the pole-zero of the closed loop transfer function is approximately as follows:

ω_{mod2_z1}＝ω_{mod2_z2}＝0；

wherein ω _{mod2_p1} is a first pole angular frequency of the second-path modulation-leg closed-loop transfer function, ω _{mod2_p2} is a second pole angular frequency of the second-path modulation-leg closed-loop transfer function, ω _{mod_p3} is a third pole angular frequency of the second-path modulation-leg closed-loop transfer function, ω _{mod2_z1} is a first zero angular frequency of the second-path modulation-leg closed-loop transfer function, ω _{mod2_z2} is a second zero angular frequency of the second-path modulation-leg closed-loop transfer function, ω _{mod2_z3} is a third zero angular frequency of the second-path modulation-leg closed-loop transfer function; the transfer function H _CL2,hf＝K_VCO2 C of the closed loop transfer function at very high frequencies; the frequency modulation transfer function of the modulation branch has a high pass characteristic as shown in fig. 4. As analyzed above, the first path modulation branch has low-pass characteristics, and the transfer function after superposition of the first path modulation branch and the second path modulation branch meets the following requirements When the parameters of the two paths of modulation branches meet/>The superimposed transfer function is reduced to H _CL＝ω_ref, as shown in FIG. 5; thus, the broadband effect can be generated, and the frequency modulation range and the frequency modulation slope can be improved.

For the fm continuous wave generator 200 shown in fig. 3, two modulation branches respectively drive one set of variable capacitors in the vco 207, and the two sets of variable capacitors reduce the phase noise of the vco 207 itself, thereby deteriorating the phase noise of the fm continuous wave generator. In addition, the variable capacitance of the second modulation branch usually has strong nonlinearity, which can deteriorate the frequency modulation linearity of the final frequency modulation continuous wave signal, and a very complex calibration mode is required to eliminate the nonlinearity of the variable capacitance, so that the calibration time is long, and the complexity and cost of the system are increased.

In order to solve the above problems, the applicant proposes a fm continuous wave generator 300, as shown in fig. 6, comprising a first modulation module 310, a second modulation module 320, a combining module 330, an oscillator module 340 and a signal processing module 350; further, a sampling module 360 is included.

The first modulation module 310 modulates the received frequency modulated continuous wave signal based on the frequency modulation codeword to obtain a first modulation voltage Vfm1.

As an example, the first modulation module 310 includes a sigma-delta modulator 311, a multi-modulus divider 312, a phase frequency detector 313, a charge pump 314, and a loop filter 315; wherein the sigma-delta modulator 311 obtains a frequency division codeword varying with time based on the frequency modulation codeword; the multi-mode frequency divider 312 is connected with the output ends of the sigma-delta modulator 311 and the oscillator module 340, performs frequency division ratio setting based on the frequency division code word, and performs frequency division on the frequency division continuous wave signal according to the frequency division ratio to obtain a frequency division signal; the phase frequency detector 313 is connected to the output end of the multi-modulus divider 312, and is used for performing phase frequency detection on the reference signal Fref and the frequency division signal Fdiv to obtain two paths of control signals; the charge pump 314 is connected with the output end of the phase frequency detector 313, and performs charge or discharge control based on two paths of control signals to obtain charge/discharge current; the loop filter 315 is connected to an output terminal of the charge pump 314, and is used for converting the charge/discharge current into the first modulation voltage Vfm1 and performing high-frequency filtering.

The sigma-delta modulator 311, the multi-modulus divider 312, the phase frequency detector 313, and the charge pump 314 are all implemented by using the existing known circuit structures, which is not limited in this embodiment; loop filter 315 is implemented as a second order filter and the capacitance of capacitor C1 is much greater than the capacitance of capacitor C2.

The second modulation module 320 performs digital-to-analog conversion on the received voltage modulation codeword to obtain a second modulation voltage Vfm2.

As an example, the second modulation module 320 includes a digital-to-analog converter 321 and a modulation filter 322, where the digital-to-analog converter 321 performs digital-to-analog conversion on the voltage modulation codeword, and then obtains the second modulation voltage Vfm2 through the modulation filter 322.

The combining module 330 is connected to the output ends of the first modulation module 310 and the second modulation module 320, and combines the first modulation voltage Vfm1 and the second modulation voltage Vfm2 based on the first combining coefficient a and the second combining coefficient b to obtain a final modulation voltage Vfm.

As an example, the combining module 330 includes a coefficient-adjustable adder, and the final modulation voltage vfm=a×vfm1+b×vfm2. The first combining coefficient a and the second combining coefficient b should be set according to actual requirements, for example, when the fm continuous wave generator 300 operates in the normal mode, the first combining coefficient a=0.2 and the second combining coefficient b=1, and when the fm continuous wave generator 300 operates in the calibration mode, the first combining coefficient a=1 and the second combining coefficient b=0.

In one possible implementation, the coefficient-adjustable adder includes a first multiplier, a second multiplier, and an accumulator; the first input end of the first multiplier is connected with the output end of the first modulation module 310 to receive the first modulation voltage Vfm1, the second input end of the first multiplier is connected with the first combining coefficient a, and the output end of the first multiplier is connected with the first input end of the accumulator; the second input end of the second multiplier is connected with the output end of the second modulation module 320 to receive the second modulation voltage Vfm2, the second input end is connected with the second combining coefficient b, and the output end is connected with the second input end of the accumulator; the output of the accumulator is used as the output of the coefficient-adjustable adder to obtain the final modulation voltage Vfm. The first combining coefficient a and the second combining coefficient b are set by the outside, for example, by the signal processing module 350, so that the first combining coefficient a and the second combining coefficient b correspond to different values in different modes, and the coefficients are adjustable.

The oscillator module 340 is connected to the output of the combining module 330, and obtains a frequency modulated continuous wave signal based on the final modulation voltage Vfm.

As an example, the oscillator module 340 includes a single variable capacitance voltage controlled oscillator that controls the variable capacitance to effect a level-to-frequency conversion by the final modulation voltage Vfm to obtain a frequency modulated continuous wave signal. Any voltage-controlled oscillator structure with a single variable capacitor can be used as the oscillator module 340, which is not limited in this embodiment.

The signal processing module 350 is configured to provide a frequency modulation codeword and a voltage modulation codeword; wherein the signal processing module 350 comprises a digital signal processor. In practice, the voltage modulation code words are in one-to-one correspondence with the frequency modulation code words, and the voltage modulation code words are digital codes corresponding to a difference voltage between a final modulation voltage Vfm (vfm=a×vfm1) formed by a first modulation voltage vfm1 corresponding to the frequency modulation code words and the sweep starting voltage Vlock 1.

The sampling module 360 is connected between the combining module 330 and the signal processing module 350, and samples the final modulation voltage Vfm through analog-to-digital conversion to obtain a sampling codeword; wherein the sampling module 360 comprises an analog-to-digital converter. In fact, the sampling module 360 is controlled by the signal processing module 350 to operate only in the calibration mode, and samples the final modulation voltage Vfm formed by the first modulation voltage Vfm1 through analog-to-digital conversion to obtain a sampled codeword.

At this time, the signal processing module 350 obtains a voltage modulation codeword based on the sampled codeword. The method comprises the following steps: the signal processing module 350 performs a difference between a sampling codeword corresponding to a final modulation voltage Vfm formed by the first modulation voltage Vfm1 and a digital codeword corresponding to a sweep initial voltage Vlock1, so as to obtain a digital codeword corresponding to a difference voltage between the two digital codewords and uses the digital codeword as a voltage modulation codeword; and establishing and storing the corresponding relation between the voltage modulation code words and the frequency modulation code words.

Correspondingly, the embodiment also provides a working method of the frequency modulation continuous wave generator, wherein the frequency modulation continuous wave generator is realized by adopting the circuit structure; the method of operation includes a normal mode.

In the normal mode, the working method of the frequency modulation continuous wave generator comprises the steps S11 to S14.

Step S11: modulating the frequency modulation continuous wave signal based on the frequency modulation code word to obtain a first modulation voltage Vfm1, wherein the slope of a frequency modulation curve corresponding to the frequency modulation code word in a normal mode is a first slope.

In practice, the signal processing module 350 provides a frequency modulated codeword with a first slope, and the first modulation module 310 modulates the frequency modulated continuous wave signal based on the frequency modulated codeword to obtain a first modulation voltage Vfm1.

Step S12: performing digital-to-analog conversion on the voltage modulation code words to obtain second modulation voltage Vfm2, wherein the voltage modulation code words correspond to the frequency modulation code words one by one; further, the voltage modulation codeword is a digital code corresponding to a difference voltage between a final modulation voltage Vfm formed by a first modulation voltage Vfm1 corresponding to the frequency modulation codeword and the sweep starting voltage Vlock 1.

In practice, the signal processing module 350 provides a voltage modulation codeword corresponding to the frequency modulation codeword, and the second modulation module 320 performs digital-to-analog conversion on the voltage modulation codeword to obtain the second modulation voltage Vfm2.

Step S13: setting a first combining coefficient a and a second combining coefficient b, wherein the first combining coefficient a and the second combining coefficient b are larger than zero, and combining the first modulation voltage Vfm1 and the second modulation voltage Vfm2 based on the first combining coefficient a and the second combining coefficient b to obtain a final modulation voltage Vfm.

In practice, the first modulation voltage Vfm1 and the second modulation voltage Vfm2 are combined by the combining block 330, where vfm=a×vfm1+b×vfm2. In addition, the first combining coefficient a and the second combining coefficient b may be set by the signal processing module 350, for example, according to practical application requirements, the signal processing module 350 sets the first combining coefficient a to 0.2 and the second combining coefficient b to 1 in the normal mode, where vfm=0.2×vfm1+vfm2.

Step S14: the frequency modulated continuous wave signal is derived based on the final modulation voltage Vfm, such as by controlling the variable capacitance in the oscillator module 340 to effect a level-to-frequency conversion to derive the frequency modulated continuous wave signal.

Further, the method of operation also includes a calibration mode; in fact, when the frequency modulation continuous wave generator works, the frequency modulation continuous wave generator enters a normal mode after entering a calibration mode; of course, for the same application scenario, the calibration mode may not be entered every time, but only once at the beginning.

In the calibration mode, the working method of the frequency modulation continuous wave generator comprises steps S21 to S23.

Step S21: the first combining coefficient a and the second combining coefficient b are regulated, so that the first combining coefficient in the calibration mode is larger than or equal to the first combining coefficient in the normal mode, and the second combining coefficient is zero; at this time, the loop bandwidth is large by controlling the variable capacitance in the oscillator module 340 only by the first modulation voltage Vfm 1.

In practice, the first combining coefficient a and the second combining coefficient b may be set by the signal processing module 350, for example, according to practical application requirements, the signal processing module 350 sets the first combining coefficient to 1 and the second combining coefficient to 0 in the calibration mode, where vfm=vfm1.

Step S22: sweep frequency is carried out based on the frequency modulation code words, and final modulation voltage Vfm formed by the first modulation voltage Vfm1 is sampled through analog-to-digital conversion, wherein the frequency modulation curve slope corresponding to the frequency modulation code words in the calibration mode is smaller than or equal to the frequency modulation curve slope corresponding to the frequency modulation code words in the normal mode; taking the second slope as an example, the slope of the frequency modulation curve corresponding to the frequency modulation code word in the calibration mode is smaller than or equal to the first slope.

In practice, the signal processing module 350 provides a frequency modulated codeword with a second slope, and the first modulation module 310 modulates the frequency modulated continuous wave signal based on the frequency modulated codeword to obtain the first modulation voltage Vfm1.

Since the second combining coefficient b in the calibration mode is zero, the final modulation voltage Vfm is related to the first modulation voltage Vfm1 only, and is independent of the second modulation voltage Vfm2, i.e., vfm=a×vfm1=vfm1; at this time, the signal processing module 350 may provide the same preset voltage modulation code word for each frequency modulation code word, however, different voltage modulation code words are also possible, and even the signal processing module 350 may control the digital-to-analog converter 321 in the second modulation module 320 to be inactive.

The sampling module 360 samples the final modulation voltage Vfm through analog-to-digital conversion to obtain a sampled codeword.

Step S13: and taking a digital code corresponding to the difference voltage between the final modulation voltage Vfm and the sweep frequency starting voltage Vlock1 as a voltage modulation code word, establishing a corresponding relation between the frequency modulation code word and the voltage modulation code word, and storing the corresponding relation.

In practice, the signal processing module 350 makes a difference between the sampled codeword corresponding to the final modulation voltage Vfm and the digital codeword corresponding to the sweep frequency starting voltage Vlock1, so as to obtain a digital codeword corresponding to the difference voltage between the two digital codewords and uses the digital codeword as the voltage modulation codeword; and establishing and storing a corresponding relation between the voltage modulation code words and the frequency modulation code words, so that the voltage modulation code words corresponding to the frequency modulation code words can be conveniently called based on the frequency modulation code words in the normal mode.

In this embodiment, the corresponding relationship between the frequency modulation codeword and the voltage modulation codeword is obtained through the calibration mode, and the second modulation module 320 is used to reproduce the difference voltage (such as Vfm1-Vlock 1) in the normal mode, so as to calibrate the variable capacitance in the oscillator module 340.

In the normal mode, the main loop formed by the first modulation module 310 adopts a smaller first combining coefficient a (e.g. a=0.2), so that the loop bandwidth is smaller, and good phase noise performance can be obtained; meanwhile, after the main loop is locked, the first modulation voltage Vfm1 is locked near Vlock2, so as to satisfy the formula Vlock 2=vlock 1×a1/a2, where Vlock1 is the sweep starting voltage, vlock2 is the locking voltage, a1 is the value of the first combining coefficient a in the calibration mode, and a2 is the value of the first combining coefficient a in the normal mode.

Inquiring the corresponding relation between the frequency modulation code words and the voltage modulation code words stored in the signal processing module 350 according to the required frequency modulation code words to obtain required voltage modulation code words; outputting the frequency modulation code word to the first modulation module 310, and synchronously outputting the voltage modulation code word to the second modulation module 320 to obtain a first modulation voltage Vfm1 and a second modulation voltage Vfm2; the combining module 330 combines the first modulation voltage Vfm1 and the second modulation voltage Vfm2 based on the first combining coefficient a and the second combining coefficient b to obtain a final modulation voltage Vfm, and controls a variable capacitor in the oscillator module 340 through the final modulation voltage Vfm to obtain a frequency-modulated continuous wave signal.

At this time, the first modulation voltage Vfm1 and the second modulation voltage Vfm2 are observed, and it is found that: the first modulation voltage Vfm1 is substantially fixed, the second modulation voltage Vfm2 follows the voltage variation corresponding to the voltage modulation codeword, and the final modulation voltage Vfm replicates the voltage waveform of the calibration phase, so that the output of the oscillator module 340 is a very linear frequency modulated continuous wave signal, as shown in fig. 7 and 8.

Correspondingly, as shown in fig. 9, the present embodiment further provides a millimeter wave radar system, which includes the fm continuous wave generator 300 described above, and further includes a millimeter wave radar chip 400; the fm continuous wave generator 300 provides an fm continuous wave signal to the millimeter wave radar chip 400, so that the millimeter wave radar chip 400 performs radar detection based on the fm continuous wave signal.

In summary, according to the frequency modulation continuous wave generator, the working method thereof and the millimeter wave radar system, through the design of the first modulation module, the second modulation module, the combining module, the oscillator module, the signal processing module and the sampling module, the combining module is utilized to combine the first modulation voltage and the second modulation voltage, so that the oscillator module with single variable capacitor is subjected to two-point modulation; in the calibration mode, the control voltage of the oscillator module (namely the final modulation voltage formed by the first modulation voltage) is sampled based on an analog-to-digital conversion mode, a digital code corresponding to the difference voltage of the sweep initial voltage is used as a voltage modulation code word, the corresponding relation between the frequency modulation code word and the voltage modulation code word is obtained, and in the normal mode, the voltage modulation code word corresponding to the frequency modulation code word is output to the second modulation module to reproduce the difference voltage, so that the calibration of the single variable capacitor in the oscillator module is realized. Therefore, the invention effectively overcomes various defects in the prior art and has high industrial utilization value.

The above embodiments are merely illustrative of the principles of the present invention and its effectiveness, and are not intended to limit the invention. Modifications and variations may be made to the above-described embodiments by those skilled in the art without departing from the spirit and scope of the invention. Accordingly, it is intended that all equivalent modifications and variations of the invention be covered by the claims, which are within the ordinary skill of the art, be within the spirit and scope of the present disclosure.

Claims

1. A frequency modulated continuous wave generator, the frequency modulated continuous wave generator comprising:

2. The frequency modulated continuous wave generator of claim 1, further comprising: the sampling module is connected between the combining module and the signal processing module, samples the final modulation voltage through analog-to-digital conversion to obtain a sampling code word, and the signal processing module obtains the voltage modulation code word based on the sampling code word.

3. The frequency modulated continuous wave generator of claim 1, wherein the first modulation module comprises:

sigma-delta modulator, multi-mode frequency divider, phase frequency detector, charge pump and loop filter;

4. The frequency modulated continuous wave generator of claim 1, wherein the second modulation module comprises: the digital-to-analog converter performs digital-to-analog conversion on the voltage modulation code word, and then obtains the second modulation voltage through the modulation filter.

5. The frequency modulated continuous wave generator of claim 1, wherein the combining module comprises a coefficient-adjustable adder.

6. The frequency modulated continuous wave generator of claim 1, wherein the oscillator module comprises a single variable capacitance voltage controlled oscillator.

7. A millimeter wave radar system comprising a frequency modulated continuous wave generator according to any one of claims 1-6.

8. A method of operating a frequency modulated continuous wave generator, the method comprising a normal mode wherein:

9. The method of operating a frequency modulated continuous wave generator according to claim 8, further comprising a calibration mode, wherein:

10. The method of claim 9, wherein the first combining coefficient in the normal mode is 0.2 and the second combining coefficient is 1; the first combining coefficient in the calibration mode is 1.