CN103888078B - Correction circuit for improving capacitance and bias characteristics of varactor diode, and equipment using the same - Google Patents

Abstract

This application discloses a kind of circuit for rectifying for improving varactor capacitance and bias characteristic, including input, outfan, low pass filter, crystal triode, the first field effect transistor, the second field effect transistor, base resistance and crystal diode.Wherein, described crystal diode is used as switch element；Described second field effect transistor is when between its drain electrode and source electrode, voltage increases, and the output voltage of described outfan keeps constant；Described first field effect transistor is for controlling the size of this output voltage values；Described second field effect transistor is at which when saturation, and the output voltage of described outfan linearly increases with input voltage.Under the effect of described circuit for rectifying, the search rate of described nuclear magnetic resonance, NMR survey field instrument is along with search voltage even variation, and field instrument is more accurate when searching for magnetic field to be measured, it is more reliable to lock during this magnetic field to be measured to make described nuclear magnetic resonance, NMR survey.The application also provides for the equipment of a kind of this circuit of application.

Description

Correction circuit for improving capacitance and bias characteristics of varactor diode, and equipment using the same

technical field

The present application relates to the technical field of voltage-controlled oscillators, in particular to a correction circuit for improving the capacitance and bias characteristics of a varactor diode. The application also relates to a voltage-controlled oscillator and a nuclear magnetic resonance field measuring instrument.

Background technique

A voltage-controlled oscillator (VCO, voltage-controlled oscillator) refers to an oscillating circuit whose output frequency corresponds to the input control voltage. The voltage controlled oscillator is one of the very important basic circuits in integrated circuits, and is widely used in various circuits. The oscillation frequency is one of the main parameters to measure the performance of the voltage-controlled oscillator. The oscillation frequency of the voltage-controlled oscillator is determined by the inductance and capacitance in the resonant circuit. In most cases, a varactor diode is used in the voltage-controlled oscillator. Adjust the oscillation frequency of the controlled oscillator.

Varactor diodes are semiconductor diodes made using the principle that the capacitance of the PN junction changes with the change of the applied reverse bias voltage. At present, it is mainly used in LC tuning circuits, electronic tuning, amplitude modulation, frequency modulation, automatic frequency control, RC filter circuits, etc. It is also used in frequency multipliers and frequency converters. Moreover, the varactor has a series of advantages such as easy adjustment, high fineness, and easy construction of an automatic tuning system.

The nuclear magnetic resonance field meter is an instrument that uses the principle of nuclear magnetic resonance to measure the magnetic field. It includes two parts: a voltage-controlled oscillator and a frequency search and lock circuit; the frequency search and lock circuit includes a frequency search circuit and a frequency lock circuit. The core of the frequency search circuit is the sawtooth wave generator, which uses the generated sawtooth wave voltage as the bias voltage of the varactor diode in the voltage controlled oscillator to realize the search for the nuclear magnetic resonance signal; the frequency locking circuit is used to lock the nuclear magnetic resonance signal; When the frequency search circuit finds a resonance signal, the frequency search circuit is disconnected, and the frequency locking circuit locks the resonance point.

The nuclear magnetic resonance field measuring instrument provided by the prior art has obvious defects when searching and locking resonance signals.

First of all, there is a nonlinear characteristic between the capacitance of the varactor diode and the bias voltage. When the bias voltage of the varactor diode is small, the capacitance is large, and the rate of change of capacitance with the bias voltage is large; when the bias voltage is large, Both the capacitance and its rate of change decrease accordingly.

Secondly, it is precisely because of the nonlinear relationship between the capacitance of the varactor diode and the bias voltage that the oscillation frequency of the voltage-controlled oscillator cannot change uniformly with the bias voltage of the varactor diode. When the oscillation frequency of the voltage-controlled oscillator reaches the resonance frequency , if the oscillation frequency of the voltage-controlled oscillator changes too quickly, it will cause the frequency search circuit to fail to lock the resonance point, which will bring difficulties to the NMR field instrument to search for the resonance frequency and lock the resonance point.

Contents of the invention

The present application provides a correction circuit for improving the capacitance and bias characteristics of the varactor diode, so as to solve the problems existing in the prior art. The present application additionally provides a voltage-controlled oscillator and a nuclear magnetic resonance field measuring instrument.

A rectification circuit for improving the capacitance and bias characteristics of a varactor diode provided by the present application includes: an input terminal, an output terminal, a low-pass filter, a transistor, a first field effect transistor, a second field effect transistor, a base pole resistors and crystal diodes;

Wherein, the input end is connected to the input side of the low-pass filter, and the output side of the low-pass filter is connected to the emitter of the transistor;

The base of the transistor is connected to the base resistor, the collector of the transistor is connected to the drain of the second field effect transistor, and the collector of the transistor is connected to the output terminal;

The source of the first field effect transistor is connected to the emitter of the transistor, the drain of the first field effect transistor is connected to the collector of the transistor, and the gate of the first field effect transistor is connected to the Drain shorted;

The gate of the second field effect transistor is short-circuited to the source, and the source of the second field effect transistor is connected to the anode of the crystal diode;

The cathode of the crystal diode is connected to the other end of the base resistor;

Crystal diodes are used as switching elements;

The second field effect transistor is used to keep the output voltage at the output end constant when the voltage between its drain and source increases; and

The first FET is used to control the magnitude of the output voltage;

The second field effect transistor is used to linearly increase the output voltage of the output terminal with the input voltage when it is in a saturated state.

Optionally, the low-pass filter includes a filter capacitor and a resistor element;

The anode of the filter capacitor is connected to the resistance element and is connected to the input side of the low-pass filter at the same time, and the other end of the resistance element is connected to the output side of the low-pass filter.

Optionally, the transistor is a PNP transistor.

Optionally, the PNP transistor is a 3CK4 PNP transistor.

Optionally, the first field effect transistor is a junction field effect transistor.

Optionally, the junction field effect transistor is a junction field effect transistor whose model is 3DJ6E.

Optionally, the second field effect transistor is a junction field effect transistor.

Optionally, the junction field effect transistor selected is a type 3DJ6G junction field effect transistor.

The present application further provides a voltage-controlled oscillator, including: an oscillation circuit and the above-mentioned correction circuit for improving the capacitance and bias characteristics of the varactor diode;

Wherein, the oscillating circuit includes a varactor diode;

The output terminal of the correction circuit is connected with the cathode of the varactor diode.

The application also provides a nuclear magnetic resonance field measuring instrument, which is characterized in that it includes: an automatic frequency search and lock circuit and the above-mentioned voltage-controlled oscillator.

Optionally, the frequency automatic search and lock circuit includes a sawtooth wave generator;

The output terminal of the sawtooth wave generator is connected with the input terminal of the correction circuit in the voltage-controlled oscillator.

Compared with the prior art, the present application has the following advantages:

One aspect of the present application provides a rectification circuit for improving the capacitance and bias voltage characteristics of the varactor diode, which solves the difficulties in searching and locking resonance signals in the prior art nuclear magnetic resonance field measuring instrument;

On the other hand, a correction circuit for improving the capacitance and bias characteristics of a varactor diode described in the present application includes: an input terminal, an output terminal, a low-pass filter, a transistor, a first field effect transistor, a second A field effect transistor, a base resistor, and a crystal diode; wherein, the input terminal is connected to the input side of the low-pass filter, and the output side of the low-pass filter is connected to the emitter of the transistor; the The base of the transistor is connected to the base resistor, the collector of the transistor is connected to the drain of the second field effect transistor, and the collector of the transistor is connected to the output terminal; the first field The source of the effect transistor is connected to the emitter of the transistor, the drain of the first field effect transistor is connected to the collector of the transistor, and the gate of the first field effect transistor is short-circuited to the drain; The gate of the second field effect transistor is short-circuited to the source, and the source of the second field effect transistor is connected to the anode of the crystal diode; the cathode of the crystal diode is connected to the other end of the base resistor connected; the crystal diode is used as a switching element; the second field effect transistor is used to keep the output voltage of the output terminal constant when the voltage between its drain and source increases; the first field effect transistor is used to control the output voltage The magnitude of the value; the second field effect transistor is used to linearly increase the output voltage of the output terminal with the input voltage when it is in a saturated state.

The correction circuit adjusts the bias voltage added to the varactor diode in the voltage-controlled oscillator, and first changes the search voltage and search frequency of the automatic frequency search and locking circuit of the nuclear magnetic resonance field measuring instrument (that is, the automatic frequency search circuit The relationship curve between the oscillation frequency of the voltage-controlled oscillator), and the relationship between the search voltage of the frequency automatic search and locking circuit and the search frequency (ie: the oscillation frequency of the voltage-controlled oscillator in the frequency automatic search circuit) The curve is an approximately linear curve. Secondly, the relationship curve between the input voltage and the search frequency when the voltage-controlled oscillator uses manual search is changed, so that the relationship between the input voltage and the search frequency when the voltage-controlled oscillator manually searches for the frequency presents an approximately linear relationship curve, even if the nuclear magnetic resonance The search frequency of the field meter varies uniformly with the input voltage.

Description of drawings

Fig. 1 is the block diagram of a kind of rectification circuit that is used to improve varactor diode capacitance and bias characteristic that the present application provides;

2 is an I/O schematic diagram of a correction circuit for improving the capacitance and bias characteristics of a varactor diode provided by the present application;

Fig. 3 is a circuit block diagram of a voltage-controlled oscillator provided by the present application;

Fig. 4 is a kind of voltage-controlled oscillator input voltage and frequency relation graph provided by the present application;

Fig. 5 is a block diagram of a nuclear magnetic resonance field measuring instrument provided by the application;

Fig. 6 is a schematic waveform diagram of a nuclear magnetic resonance field measuring instrument provided by the present application.

detailed description

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the application. However, the present application can be implemented in many other ways different from those described here, and those skilled in the art can make similar promotions without violating the connotation of the present application. Therefore, the present application is not limited by the specific implementation disclosed below.

The application provides a correction circuit for improving the capacitance and bias characteristics of the varactor diode; in addition, the application further provides a voltage-controlled oscillator and a nuclear magnetic resonance field measuring instrument.

An embodiment corresponding to a correction circuit for improving the capacitance and bias characteristics of a varactor diode is as follows:

Referring to FIG. 1-FIG. 2, it shows a rectification circuit provided by this embodiment for improving the capacitance and bias characteristics of the varactor diode. include:

Fig. 1 is a kind of block diagram that is used to improve the rectification circuit of varactor capacitance and bias voltage characteristic that the present embodiment provides;

FIG. 2 is an I/O schematic diagram of a correction circuit for improving the capacitance and bias characteristics of a varactor diode provided by this embodiment.

Referring to FIG. 1 , it shows a block diagram of a correction circuit for improving the capacitance and bias characteristics of a varactor diode provided by this embodiment.

The correction circuit is composed of a low-pass filter 110 , a transistor 120 , a first field effect transistor 130 , a second field effect transistor 140 , a base resistor 150 , a crystal diode 160 , an input terminal 170 and an output terminal 180 .

The low-pass filter 110 is used to filter the input voltage VI input from the input terminal 170 .

The low-pass filter 110 includes a filter capacitor 111 and a resistor element 112 .

The anode of the filter capacitor 111 is connected to one end of the resistance element 112, and the cathode is grounded;

One end of the resistance element 112 and the anode of the filter capacitor 111 are connected to the input side of the low-pass filter 10 at the same time, and the other end of the resistance element 112 is connected to the output side of the low-pass filter 110 .

The transistor 120 is used to provide a current proportional to the input voltage VI of the input terminal 170 .

The emitter of the transistor 120 is connected to the output side of the low-pass filter 110 , the base is grounded through the base resistor 150 , and the collector is connected to the drain of the second field effect transistor 140 .

In this embodiment, the transistor 120 is a PNP transistor, and a PNP transistor of model 3CK4 is selected.

The first field effect transistor 130 is used to provide a small constant current to the second field effect transistor 140 .

The source and drain of the first field effect transistor 130 are connected in parallel with the emitter and collector of the transistor 120 , and the gate of the first field effect transistor 130 is short-circuited with the drain.

In this embodiment, the first field effect transistor is a junction field effect transistor, and a junction field effect transistor with a model of 3DJ6E is selected.

The second field effect transistor 140 is used for providing the output voltage VO of the output terminal 180 .

The output voltage VO of the output terminal 180 is connected from the drain of the second field effect transistor 140, and the drain of the second field effect transistor 140 is connected to the collector of the transistor 120, and the source is connected to the transistor. The anode of the diode 160 is connected to the source with the gate connected.

In this embodiment, the second field effect transistor is a junction field effect transistor, and the type of junction field effect transistor is 3DJ6G.

The crystal diode 160 serves as a switching element.

The anode of the crystal diode 160 is connected to the source of the second field effect transistor 140 , and the cathode is grounded.

In this embodiment, the crystal diode 160 is a crystal diode whose model is 2CK2.

Referring to FIG. 2 , it shows an I/O schematic diagram of a correction circuit for improving the capacitance and bias characteristics of a varactor diode provided by this embodiment.

The curve L1 is the relationship curve between the input voltage VI of the input terminal 170 and the output voltage VO of the output terminal 180 without the above correction circuit. At this time, the output voltage VO is the input voltage VI, that is, the relationship curve L1 between the input voltage VI and the output voltage VO is straight line;

The curve L2 is a relationship curve between the input voltage VI of the input terminal 170 and the output voltage VO of the output terminal 180 of the correction circuit for improving the capacitance and bias characteristics of the varactor diode described in this embodiment;

When the input voltage VI of the input terminal 170 is small (0<VI<V1), the crystal diode 160 is not turned on, and the crystal diode 160 is in a state of high resistance, at this time, the output voltage VO is approximately equal to the input voltage VI, Just form the shape of the curve L2 in area 1;

When the input voltage VI value of the input terminal 170 is in the middle of V1 and V2 (V1<VI<V2), as the input voltage VI increases, the crystal diode 160 is turned on, and the drain and source of the second field effect transistor 140 The voltage UDS at both ends of the pole also increases accordingly. With the increase of the voltage UDS at both ends of the drain and source of the second field effect transistor 140, the conductive channel inside the second field effect transistor 140 gradually widens. The value of the current IDS at both ends of the drain and the source increases. At this time, the output voltage VO increases slowly, forming the shape of the curve L2 in area 2;

In addition, the role of the first field effect transistor 130 at this time is to provide a small constant current to the second field effect transistor 140 to adjust the height of the curve L2 in the region 2;

When the input voltage VI of the input terminal 170 is large (V2<VI), as the input voltage VI continues to increase, the second field effect transistor 140 is in a saturated state, that is, as the drain of the second field effect transistor 140 As the voltage UDS at both ends of the pole and the source increases, the value of the current IDS flowing through the drain and the source of the second field effect transistor 140 remains unchanged. At this time, the output voltage VO follows the input voltage VI The linear change forms the shape of the curve L2 in the area 3.

A corresponding embodiment of a voltage-controlled oscillator is as follows:

Referring to FIG. 3-FIG. 4, it shows a voltage-controlled oscillator provided by this embodiment. include:

Fig. 3 is a circuit block diagram of a voltage-controlled oscillator provided in this embodiment;

FIG. 4 is a graph showing the relationship between input voltage and frequency of a voltage-controlled oscillator provided in this embodiment.

Referring to FIG. 3 , it shows a circuit block diagram of a voltage-controlled oscillator provided by this embodiment.

The voltage controlled oscillator includes a correction circuit 100 and an oscillation circuit 200 .

Correction circuit 100, where the correction circuit 100 refers to a correction circuit for improving the capacitance and bias characteristics of the varactor diode described in the embodiment corresponding to the above-mentioned one for improving the capacitance and bias voltage of the varactor diode characteristics of the correction circuit.

An oscillation circuit 200 , the oscillation circuit 200 includes a varactor diode 210 , an input terminal 220 , a probe inductance coil 230 , a detection amplifier circuit 240 , a main oscillation circuit 250 and a frequency measurement circuit 260 .

For the detailed introduction of the correction circuit 100, reference may be made to the above-mentioned embodiments.

In this embodiment, the input voltage VI of the input terminal 170 of the correction circuit is the input voltage VIO of the voltage-controlled oscillator;

The output terminal 180 of the correction circuit 100 is connected to the input terminal 220 of the oscillation circuit 200, and the input terminal 220 of the oscillation circuit 200 is connected to the cathode of the varactor diode 210, then the output terminal 180 of the correction circuit 100 The output voltage VO of the oscillating circuit 200 is the input voltage of the oscillating circuit 200 ; furthermore, the output voltage VO of the output terminal 180 of the rectifying circuit 100 is the bias voltage VR of the varactor diode 210 in the oscillating circuit 200 .

Referring to FIG. 4 , it shows a graph of the relationship between input voltage and frequency of a voltage-controlled oscillator provided by this embodiment.

FIG. 4 is a graph showing the relationship between the input voltage VIO of the input terminal 170 of the voltage-controlled oscillator (Oscillator) and the oscillation frequency (Oscillation Frequency) FO.

Wherein, the dotted line in the figure represents the curve drawn by the actual data of the input voltage VIO of the voltage-controlled oscillator input terminal 170 and the oscillation frequency (Oscillation Frequency) FO;

The solid line represents the curve formed by linear fitting of the relationship between the input voltage VIO at the input terminal 170 of the voltage-controlled oscillator and the oscillation frequency FO, namely: the input voltage VIO at the input terminal 170 of the voltage-controlled oscillator and the oscillation frequency FO There is an approximately linear relationship between them.

A corresponding embodiment of a nuclear magnetic resonance field measuring instrument is as follows:

Referring to Fig. 5-Fig. 6, it shows a nuclear magnetic resonance field measuring instrument provided by this embodiment.

Wherein, Fig. 5 is a block diagram of a nuclear magnetic resonance field measuring instrument provided in this embodiment;

Fig. 6 is a schematic waveform diagram of a nuclear magnetic resonance field measuring instrument provided in this embodiment.

Referring to FIG. 5 , it shows a block diagram of a nuclear magnetic resonance field measuring instrument provided in this embodiment.

A nuclear magnetic resonance field measuring instrument provided by the present application includes a frequency automatic search and lock circuit and the above-mentioned voltage-controlled oscillator.

The nuclear magnetic resonance field measuring instrument can use an automatic mode and a manual mode to measure the magnetic field. Automatic mode is to use the adjusted voltage generated by the frequency automatic search and lock circuit as the bias voltage of the varactor diode of the voltage controlled oscillator to realize automatic frequency search and lock; manual mode is to directly adjust the adjustable potentiometer manually, and the adjustable potentiometer The regulated voltage is used as the bias voltage for the VCO varactor diode.

The automatic frequency search and lock circuit includes an automatic frequency search circuit and an automatic frequency lock circuit.

The core of the frequency automatic search circuit is a sawtooth wave generator. The sawtooth wave generator is used to generate a sawtooth wave voltage, and output the sawtooth wave voltage as an output voltage; the output end of the sawtooth wave voltage is connected to the input end of the voltage controlled oscillator (that is: in the voltage controlled oscillator An input terminal 170 of a correction circuit for improving the capacitance and bias characteristics of the varactor diode);

The frequency automatic locking circuit is used to lock the resonance point.

When the frequency of the automatic frequency search circuit reaches the measured magnetic field, a nuclear magnetic resonance signal appears. At this time, the automatic frequency search circuit is disconnected, no longer searches, and the automatic frequency locking circuit starts to work, and the resonance point (that is: the occurrence of nuclear magnetic resonance signal) to lock.

Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the present application. Any person skilled in the art can make possible changes and modifications without departing from the spirit and scope of the present application. Therefore, the present application The scope of protection should be based on the scope defined by the claims of this application.

Claims (11)

1. A correction circuit for improving varactor capacitance and bias characteristics, characterized in that it comprises: input terminal, output terminal, low-pass filter, crystal triode, first field effect transistor, second field effect transistor, base resistor and crystal diode; Wherein, the input end is connected to the input side of the low-pass filter, and the output side of the low-pass filter is connected to the emitter of the transistor; The base of the transistor is connected to the base resistor, the collector of the transistor is connected to the drain of the second field effect transistor, and the collector of the transistor is connected to the output terminal; The source of the first field effect transistor is connected to the emitter of the transistor, the drain of the first field effect transistor is connected to the collector of the transistor, and the gate of the first field effect transistor is connected to the Drain shorted; The gate of the second field effect transistor is short-circuited to the source, and the source of the second field effect transistor is connected to the anode of the crystal diode; The cathode of the crystal diode is connected to the other end of the base resistor; Crystal diodes are used as switching elements; The second field effect transistor is used to keep the output voltage at the output end constant when the voltage between its drain and source increases; and The first FET is used to control the magnitude of the output voltage; The second field effect transistor is used to linearly increase the output voltage of the output terminal with the input voltage when it is in a saturated state; The output terminal is connected with the cathode of the varactor diode. 2. A kind of correction circuit for improving varactor capacitance and bias voltage characteristic according to claim 1, is characterized in that, described low-pass filter comprises filter capacitor and resistive element; The anode of the filter capacitor is connected to the resistance element and is connected to the input side of the low-pass filter at the same time, and the other end of the resistance element is connected to the output side of the low-pass filter. 3. A correction circuit for improving the capacitance and bias characteristics of the varactor diode according to claim 1, wherein the transistor is a PNP transistor. 4. A rectifying circuit for improving the capacitance and bias characteristics of varactor diodes according to claim 3, wherein the PNP transistor is a PNP transistor of the type 3CK4. 5 . The correction circuit for improving the capacitance and bias characteristics of the varactor diode according to claim 1 , wherein the first field effect transistor is a junction field effect transistor. 6 . The correction circuit for improving the capacitance and bias characteristics of the varactor diode according to claim 5 , wherein the junction field effect transistor is a junction field effect transistor whose model is 3DJ6E. 7 . The correction circuit for improving the capacitance and bias characteristics of the varactor diode according to claim 1 , wherein the second field effect transistor is a junction field effect transistor. 8 . The rectifying circuit for improving the capacitance and bias characteristics of the varactor diode according to claim 7 , wherein the junction field effect transistor is 3DJ6G junction field effect transistor. 9. A voltage-controlled oscillator, characterized in that it comprises: an oscillating circuit and a correction circuit for improving the capacitance and bias characteristics of a varactor diode according to any one of claims 1 to 5; Wherein, the oscillating circuit includes a varactor diode; The output terminal of the correction circuit is connected with the cathode of the varactor diode. 10. A nuclear magnetic resonance field measuring instrument, characterized in that it comprises: an automatic frequency search and lock circuit and a voltage-controlled oscillator as claimed in claim 9. 11. A nuclear magnetic resonance field measuring instrument according to claim 10, wherein the frequency automatic search and lock circuit includes a sawtooth wave generator; The output terminal of the sawtooth wave generator is connected with the input terminal of the correction circuit in the voltage-controlled oscillator.