JP2008205876A - Output level control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an output level control circuit to increase speed up to a response limit of a continuous variable attenuator even when any level value is set. <P>SOLUTION: The output level control circuit which attenuates a radio high-frequency signal to be input in the continuous variable attenuator 4 by a prescribed attenuation based on a level setting signal, detects the radio frequency signal to be output from the continuous variable attenuator 4 by a level detector 6, and feedback-controls the detected level detecting signal so as to follow the level setting signal, is provided with a nonlinear correction circuit 7 to output a signal with compensated nonlinear characteristics of the continuous variable attenuator 4 to the continuous variable attenuator 4 based on a difference signal between the level setting signal and the level detecting signal. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an output level control circuit for a high frequency signal of several MHz or more, which can be applied to a local signal section for a down converter of a signal generator or a spectrum analyzer.

  An output level control circuit used for a high-frequency signal generator or the like compares a detection means for detecting an output level of a high-frequency signal output from an amplifying unit with an output of the detection means and a reference voltage corresponding to a predetermined output level. By means of a comparison means and an automatic level adjustment means for controlling the output level of the amplifier in response to the output of the comparison means, the output level is kept constant even with respect to ambient temperature changes and the like. .

FIG. 5 is a block diagram showing the configuration of a conventional output level control circuit. The level setting circuit 1 performs output power setting, and outputs a voltage value corresponding to the output power from the DA converter as a level setting value according to the voltage-to-power table. The subtraction circuit 2 includes an addition circuit and the like, compares the level setting value output from the level setting circuit 1 with the level output value output from the level detector 6, and outputs the difference signal. The loop filter 3 is composed of an active filter including an integration circuit, and receives the difference signal output from the subtraction circuit 2. The continuously variable attenuator 4 uses a PIN diode and attenuates an RF (radio high frequency) signal input by an attenuation controlled by a signal output from the loop filter 3. The power divider 5 splits the RF signal output from the continuously variable attenuator 4 into two. One RF signal whose power has been branched by the power divider 5 is output to the outside. The level detector 6 detects the other RF signal whose power has been branched by the power divider 5 and outputs a corresponding level detection signal. The level detection signal is fed back to the input of the subtraction circuit 2.

  The operation of the output level control circuit of FIG. The level setting signal output from the level setting circuit 1 is compared with the level detection signal output from the level detector 6 by the subtraction circuit 2, and the difference signal is input to the loop filter 3. The continuous variable attenuator 4 attenuates the RF signal input to the continuous variable attenuator 4 with a predetermined attenuation controlled by the output signal of the loop filter 3. The RF signal output from the continuously variable attenuator 4 is split in two directions by the power divider 5, one becomes the RF signal output of the output level control circuit, and the other is input to the level detector 6. The level detection signal output from the level detector 6 is fed back to the inverting input terminal of the subtraction circuit 2. As described above, since the loop filter 3 includes the integration circuit, feedback control is performed so that an offset does not occur in the difference signal between the level setting signal and the level detection signal.

  Prior art documents related to the output level control circuit include the following.

JP 2006-157201 A

  In the conventional output level control circuit, the continuously variable attenuator 4 uses a plurality of PIN diodes whose resistance to the RF signal is approximately inversely proportional to the forward current, and these are connected in series and in parallel to form a π-type attenuator and Since the T-type attenuator is configured, a large non-linear characteristic exists in the control signal to attenuation (logarithm) ratio characteristic.

  FIG. 6 is a characteristic curve diagram showing an example of the characteristic of the continuously variable attenuator 4 composed of a PIN diode. When the attenuation amount is large, the variable amount per unit control voltage becomes large, and there is a difference of about 500 times when the sensitivity near the attenuation amount of -5 dB and -30 dB is compared.

  As described above, when the feedback loop shown in FIG. 5 is configured in a state where the sensitivity difference is 500 times, for example, if the loop band when the set value is set to −5 dB is designed to 5 kHz, the loop band is set to −30 dB. Becomes 2.5 MHz. Since the PIN diode has a carrier life determined at the time of device design, if the frequency of the input RF signal is 100 MHz, for example, the time constant itself needs to be about 1 μs. Therefore, the high-speed response to the control voltage required for setting the loop band to 2.5 MHz cannot be expected.

  As a result, the response of the output level control circuit varies by a factor of 500 depending on the set attenuation amount. In such a situation, since the level responsiveness of the signal generator varies depending on the level setting value, there is a problem that it cannot be used for an application that requires a high-speed response in all level settings.

  An object of the present invention is to provide an output level control circuit capable of speeding up to the response limit of a continuously variable attenuator at any level setting value.

In order to achieve such a problem, an output level control circuit according to the invention described in claim 1 of the present invention includes:
A radio high-frequency signal input to the continuous variable attenuator is attenuated by a predetermined attenuation based on the level setting signal, and a radio frequency signal output from the continuous variable attenuator is detected by the level detector, and the detected level is detected. In an output level control circuit that feedback-controls a signal to follow the level setting signal,
A non-linear correction circuit is provided that outputs a signal obtained by compensating the non-linear characteristic of the continuous variable attenuator to the continuous variable attenuator based on a difference signal between the level setting signal and the level detection signal.
It is provided with.

The invention according to claim 2
The output level control circuit according to claim 1.
The nonlinear correction circuit is an exponential amplifier using a voltage-current characteristic of a diode.

  As is apparent from the above description, according to the present invention, the radio high-frequency signal input to the continuous variable attenuator is attenuated by a predetermined attenuation amount based on the level setting signal and output from the continuous variable attenuator. In an output level control circuit that detects a radio high-frequency signal with a level detector and feedback-controls the detected level detection signal so as to follow the level setting signal, a difference signal between the level setting signal and the level detection signal is obtained. A non-linear correction circuit that outputs to the continuous variable attenuator a signal that compensates for the non-linear characteristics of the continuous variable attenuator based on this can reduce the sensitivity change due to the level setting value, and continuously variable attenuation at any level setting value It is possible to provide an output level control circuit capable of speeding up to the response limit of the device.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration block diagram showing an example of an output level control circuit according to an embodiment of the present invention. The same parts as those in FIG.

  The nonlinear correction circuit 7 receives a signal output from the loop filter 3 and controls the attenuation amount of the continuous variable attenuator 4 by the output signal.

  Corresponding to the output signal of the loop filter 3, the nonlinear correction circuit 7 outputs a compensated signal to the continuously variable attenuator 4 so as to cancel the nonlinear characteristic of the continuously variable attenuator 4.

  FIG. 2 is a configuration circuit diagram showing a specific example of the nonlinear correction circuit 7, which is constituted by an exponential function amplifier. The diode D1 has an anode terminal connected to the input terminal 71 of the nonlinear correction circuit 7 and a cathode terminal connected to the inverting input terminal of the operational amplifier 72. The non-inverting input terminal of the operational amplifier 72 is connected to the common, and a resistor R1 is connected between the non-inverting input terminal and the output terminal. The output terminal of the operational amplifier 72 is connected to the output terminal 73 of the nonlinear correction circuit 7.

但し、Is：逆方向飽和電流、q：電気素量、k：ボルツマン定数、T：温度
すなわち、ダイオードのＩ−Ｖ特性を利用することにより、指数関数による補正をハードウエアで行うことができる。 The operation of the circuit of FIG. 2 will be described below. In general, the IV characteristic of a diode is expressed by the Ebers-Moll equation (the following equation).

However, Is: reverse saturation current, q: elementary electric charge, k: Boltzmann constant, T: temperature, that is, correction by an exponential function can be performed by hardware using the IV characteristics of the diode.

  2 is used as the diode D1 of the exponential amplifier shown in FIG. 2, and when the feedback resistance R1 is 470 kΩ, the attenuation of the RF signal by the continuous variable attenuator 4 is input to the nonlinear correction circuit 7 ( That is, the characteristic seen from the control voltage is as shown in FIG. By this correction, the sensitivity difference which was 500 times can be reduced to 5 times. As a result, at any level setting, the loop bandwidth can be suppressed to a change of about 5 times, and the variation in response to the level setting is reduced.

  According to the output level control circuit configured as described above, the non-linear correction circuit 7 compensates for the non-linear characteristic of the continuously variable attenuator, thereby making it possible to reduce the sensitivity change due to the level setting value and continuously changing the level setting value. It is possible to provide an output level control circuit capable of speeding up to the response limit of the attenuator.

  In the above embodiment, an exponential function amplifier is used as the nonlinear correction circuit 7. However, the present invention is not limited to this, and other types of nonlinear correction circuits such as a broken line approximation circuit may be used.

It is a block diagram showing an example of an output level control circuit according to an embodiment of the present invention. 3 is a configuration circuit diagram showing a specific example of a nonlinear correction circuit 7. FIG. It is a characteristic curve figure which shows the current-voltage characteristic of a diode. It is a characteristic curve figure which shows the nonlinear characteristic of the output level control circuit after compensation. It is a block diagram showing a conventional example of an output level control circuit. It is a characteristic curve figure which shows the nonlinear characteristic of the conventional output level control circuit.

Explanation of symbols

4 Continuously variable attenuator 6 Level detector 7 Nonlinear correction circuit D1 Diode

Claims (2)

A radio high-frequency signal input to the continuous variable attenuator is attenuated by a predetermined attenuation based on the level setting signal, and a radio frequency signal output from the continuous variable attenuator is detected by the level detector, and the detected level is detected. In an output level control circuit that feedback-controls a signal to follow the level setting signal,
An output level comprising: a non-linear correction circuit that outputs a signal obtained by compensating non-linear characteristics of the continuous variable attenuator to the continuous variable attenuator based on a difference signal between the level setting signal and the level detection signal. Control circuit. 2. The output level control circuit according to claim 1, wherein the nonlinear correction circuit is an exponential amplifier using a voltage-current characteristic of a diode.

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