JP2001044763A - Detection circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a detection circuit that has a wide input dynamic range. SOLUTION: The detection circuit consists of a simple circuit provided with a detector 40 that receives an input signal, detects the input signal and outputs a detected voltage and with an attenuator 50 that is operated by using the detected voltage for its bias voltage. Increasing the attenuation of the attenuator 50 attended with an increase in the input power to the detection circuit can limit the increase in the input power to a diode 43 being a detection element. Thus, the input power dynamic range of the detection circuit can be widened by decreasing the increase in the input power to the diode in comparison with the increase in the input power to the detection circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a detection circuit, and more particularly to a detection circuit suitable for monitoring input high frequency power.

[0002]

2. Description of the Related Art When monitoring the power level of a high frequency (RF) signal such as a transmission / reception signal of a radio transceiver or the like, the RF signal is detected (or rectified) using a detection circuit to convert an AC signal. It is common to measure the amplitude as a DC signal.

FIG. 4 shows an example of such a detection circuit. That is, a detector 10 to which an input signal (RF) is input;
It comprises a differential amplifier 20 and a reference voltage generation circuit 30. The detector 10 includes a diode 11, a π-type filter (low-pass filter) 12 including an inductor and a capacitor, and voltage dividing resistors 13 and 14. Also,
The differential amplifier 20 includes an operational amplifier 21 and a non-inverted (+)
Input resistance connected between the input terminal and the output terminal of the detector 10
Rs, a feedback resistor Rf connected between the inverting (-) input terminal and the output terminal, and voltage dividing resistors Rs and Rf for dividing the output Vref of the reference voltage generating circuit 30 and applying the divided voltage to the inverting input terminal of the amplifier 21. You. An output voltage Vout is output from the output terminal of the differential amplifier 20. Further, the reference voltage generating circuit 30 includes a voltage dividing resistor 3
1 and 32.

[0004] An input signal (RF) having an input power Pin to be monitored is input to a detector 10, and a detection voltage Vdet appears between a connection point of the resistors 13 and 14 and ground, that is, at both ends of the resistor 14. The differential amplifier 20 has the detection voltage Vdet described above and a predetermined reference voltage Vr from the reference voltage generation circuit 30.
Amplify ef differences.

FIG. 5 is a graph showing the magnitude of the input power Pin of the input signal (RF) of the detection circuit of FIG. 4 and the characteristics of the detection voltage Vdet and the reference voltage Vref. FIG. 6 is a graph showing characteristics of the output voltage Vout of the differential amplifier 20 in FIG.

As shown in FIG. 5, a detection voltage Vdet output from the detector 10 changes nonlinearly according to the magnitude of the input power Pin. Also, the output voltage Vout of the differential amplifier 20
Also varies non-linearly. In the detector 1, the maximum input level that can be input to the diode 11 for detecting the input signal (RF) is the input level when the detection voltage Vdet is equal to the sum of the reverse voltage Vr and the forward voltage Vf of the diode 11. It is. Therefore, the input range of the input power Pin that can be detected, that is, the dynamic range Pd is the range shown in FIG.

A conventional technique for expanding the dynamic range Pd is disclosed in Japanese Patent Application Laid-Open No. Sho 62-60321 entitled "Output Power Control Device for Transmitter". In this prior art, a switch circuit is arranged in front of the detector, and the amount of attenuation of the attenuator is switched and output according to an external control signal, thereby controlling the detection voltage Vdet and expanding the dynamic range Pd. I'm trying.

[0008]

The above-mentioned prior art has several problems. First, the maximum input power input to the detection circuit is controlled by the reverse voltage Vr of the diode used for the detection element, and if the excessive input power is sufficiently high for the power range to be monitored, the dynamic The range cannot be expanded. The reason is that the detection voltage increases in a square characteristic with an increase in the input power, and furthermore, the maximum detection voltage is damaged unless the reverse voltage Vr of the diode used for the detection element is made smaller, so that the diode is damaged.
This is because the maximum input power is limited.

Second, since the switch circuit is provided in the preceding stage of the detector, the output detection voltage tends to be discontinuous or unstable when the switch is switched, and is not suitable as a level detection detector. It is. Further, when a follow-up speed of the detection voltage is required, a high-speed control signal for switching the switch circuit is required. The reason is that it is difficult to output a voltage continuously and at high speed because the amount of attenuation of the attenuator is digitally changed by a switch.

An object of the present invention is to provide a detection circuit having a wide input power dynamic range.

[0011]

In order to solve the above-mentioned problems, a detection circuit according to the present invention employs the following characteristic configuration.

(1) In a detection circuit for detecting a high-frequency input signal using a detection diode to obtain a detection voltage, an attenuator is provided before and after the detection diode, and the amount of attenuation of the attenuator is obtained by the detection voltage. Detection circuit controlled by bias voltage.

(2) A capacitor and a PI as the attenuator
The detection circuit according to the above (1) using an L-shaped attenuator using an N diode.

(3) The detection circuit according to (1), wherein the bias voltage is obtained by a DC amplifier that amplifies the detection voltage.

(4) The detection circuit according to (2) or (3), wherein the bias voltage of the DC amplifier is applied to the PIN diode via a bias resistor.

(5) The detection circuit according to (4), wherein the bias resistance value is adjusted to linearize an input signal level-detection voltage characteristic of the detection circuit.

(6) The detection circuit according to (2), wherein a parallel capacitor is connected to the PIN diode.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The construction and operation of a preferred embodiment of a detection circuit according to the present invention will be described below in detail with reference to the accompanying drawings.

FIG. 1 is a circuit diagram of a preferred embodiment of a detection circuit according to the present invention. This detection circuit includes an attenuator 50 to which a high-frequency signal Pin is input, a detector 40 connected to a subsequent stage, and a DC amplifier 60 that amplifies the output Vdet and feeds back to the attenuator 50.

The attenuator 50 is connected between the input and output terminals thereof, a capacitor 55 connected in series, and connected between the output terminal and ground.
It includes a PIN diode 54, a capacitor 53 connected in parallel with the PIN diode 54, and a series circuit of an inductor 52 and a resistor 51 that feeds back the output voltage Vb of the DC amplifier 60 at an output terminal. The detector 40 includes a DC blocking capacitor 41 connected in series to the output terminal of the attenuator 50, a detection diode 43 connected between the output side of the capacitor 41 and the output terminal of the detector 40, and both ends of the diode 43. , And an inductor 42 and a resistor 44 connected between the ground and the ground.

Next, FIG. 2 shows a characteristic curve of the high-frequency input power (Pin) and the detection output Vdet of the detector 40 in comparison with the characteristic curve of the prior art. FIG. 3 shows the DC amplifier 60 in FIG.
And the attenuation characteristic curve of the attenuator 50.

Next, the operation of the detection circuit of FIG. 1 will be described with reference to FIGS. The high-frequency signal Pin input to the input terminal of the attenuator 50 is detected by the diode 43 of the detector 40 via the capacitor 55, and is output to the output terminal thereof as a detection voltage Vdet. The detection voltage Vdet is used as an output of the detection circuit, and is amplified by the DC amplifier 60 and is fed back to the PIN diode 54 of the attenuator 50 via the resistor 51 and the inductor 52. The amount of attenuation of the attenuator 50 is variably controlled by the bias voltage Vb. Accordingly, the signal level of the high-frequency input signal Pin input to the input terminal is attenuated by the attenuator 50 by the amount of attenuation corresponding to the bias voltage Vb and output from the attenuator 50, and the DC component is blocked (removed) by the capacitor 41. After that, only the high-frequency signal component is detected by the detection diode 43.

When the bias voltage Vb is applied to the attenuator 50, the amount of attenuation changes nonlinearly as shown in FIG. 3 according to the bias voltage Vb. Further, the change characteristic of the attenuation amount of the attenuator 50 differs with the change of the resistance value Rb of the resistor 51. Here, the attenuator 5 when Rb is selected as Rb1, Rb2 and Rb3
The characteristic curves of the attenuation amount of 0 are shown in (a), (b) and (c), respectively. Note that Rb1 <Rb2 <Rb3.

Next, when the input level of the high-frequency input signal Pin increases, the detection voltage Vdet detected by the detector 40 increases. On the other hand, the detection voltage Vdet is input to the DC amplifier 60 and amplified, and the bias voltage Vb is obtained to obtain the bias voltage Vb.
, The attenuation of the attenuator 50 also increases. At this time, by setting the attenuation amount of the attenuator 50 increased by the increased bias voltage Vb smaller than the increase amount of the input level of the attenuator 50, the increase amount of the level input to the detector 40 is reduced. Can be. In other words,
Even if the input level of the high-frequency signal input to the input terminal increases, the signal level input to the detector 40 is attenuated by the attenuator 50 and gradually increases.

The maximum input level of the detection circuit is determined by the detector 40
And the reverse voltage and forward voltage of the detection diode 43 constituting That is, the detection voltage Vdet is the reverse voltage Vr of the diode 43.
If it is not smaller than the sum of
Therefore, the maximum input level of the detection circuit is an input level at which the detection voltage Vdet is equal to the sum (Vr + Vf) of the reverse voltage Vr of the diode 43 and the forward voltage Vf. Here, as apparent from comparison of the characteristic curve of FIG. 2, particularly the characteristic curve (a) of the detection circuit according to the present invention with the characteristic curve (b) of the conventional circuit, the maximum input level of the detection circuit according to the present invention is ,
It becomes larger than the maximum input level of the conventional circuit. The reason is that, as is apparent from the above description, even if the input level of the high-frequency input signal at the input terminal increases, the input level to the detector 40 is controlled by the attenuator 50, so that the input dynamic range can be widened. Because we can. Bias resistance Rb
Is adjusted (selected) to linearize the detection circuit.

The configuration and operation of the preferred embodiment of the detection circuit according to the present invention have been described above in detail. However, the present invention should not be limited to only such specific examples, and those skilled in the art can easily understand that various modifications can be made without departing from the gist of the present invention.

[0027]

As can be understood from the above description, according to the detection circuit of the present invention, the dynamic range of the input level can be widened, so that a wide range of input signal levels can be effectively detected and monitored. Becomes possible. The reason is that when the input level at the input terminal increases, the attenuation of the attenuator increases, so that the increase in the input signal level input to the detector diode is limited.

Further, according to the detection circuit of the present invention, it is possible to obtain a detection output more faithfully with respect to a wide range of input signal levels. The reason is that generally, the input signal level versus the detection output characteristic of the detection diode becomes non-linear due to the nonlinear characteristic of the diode. However, by utilizing the non-linear attenuation characteristics of the attenuator diode, a more linear input signal level versus detection voltage characteristic can be obtained. Further, by adjusting the resistance Rb for inputting the bias voltage Vb to the diode of the attenuator, it is possible to further linearize the input signal level versus the detection voltage characteristic, which has a remarkable effect in practical use.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of a preferred embodiment of a detection circuit according to the present invention.

FIG. 2 is a graph showing an input signal level versus a detection voltage characteristic curve of the detection circuit of FIG. 1 and a conventional circuit.

FIG. 3 is a characteristic curve of bias voltage versus attenuation of the detection circuit of FIG. 1;

FIG. 4 is a circuit diagram of an example of a conventional detection circuit.

FIG. 5 is a characteristic diagram of an input signal level, a detection voltage, and a reference voltage of the detection circuit of FIG. 4;

FIG. 6 is a characteristic curve of an input power Pin to a detection voltage of a detection diode.

[Explanation of symbols]

 40 detector 43 detector diode 50 attenuator 51 bias resistor (Rb) 53, 55 capacitor 54 PIN diode

Claims (6)

[Claims] 1. A detection circuit for detecting a high-frequency input signal using a detection diode to obtain a detection voltage, wherein an attenuator is provided before and after the detection diode, and the amount of attenuation of the attenuator is obtained by the detection voltage. A detection circuit characterized by being controlled by voltage. 2. The detection circuit according to claim 1, wherein an L-shaped attenuator using a capacitor and a PIN diode is used as the attenuator. 3. The detection circuit according to claim 1, wherein the bias voltage is obtained by a DC amplifier that amplifies the detection voltage. 4. The detection circuit according to claim 2, wherein the bias voltage of the DC amplifier is applied to the PIN diode via a bias resistor. 5. The detection circuit according to claim 4, wherein said bias resistance value is adjusted to linearize an input signal level-detection voltage characteristic of said detection circuit. 6. The detection circuit according to claim 2, wherein a parallel capacitor is connected to said PIN diode.