JPS61150404A - Amplitude control circuit - Google Patents

Abstract

PURPOSE:To obtain an amplitude control circuit having a wide dynamic range and high linearity by inserting the entire part of a differential amplifier to a feedback circuit of an operational amplifier to a feedback circuit of an operational amplifier and also having a collector current proportional to the level of a DC or AC control signal when the transistor constituting said differential amplifier conducts. CONSTITUTION:The base electrodes of a pair of transistors (TR) 11 and 13 form the input terminal 12 and 14 of the alternating signals. Thus a differential amplifier 1 is obtained. The load resistors 15 and 17 are connected to the collector electrodes of both TR 11 and 13 respectively. The collector electrode of the TR13 is connected to an output terminal 18. A reverse input terminal 2 of an operational amplifier 21 is connected to an input terminal 22 of a DC control signal Vc via a resistor 23 as well as to a common connection point 16 of both resistors 15 and 17. The output terminal of the amplifier 21 is connected to a common emitter electrode of both TRs 11 and 13 via a resistor 25. Thus this amplitude control circuit contains no wave detector and therefore has a wide dynamic range.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an amplitude control circuit that obtains an alternating signal proportional to the magnitude of a DC or AC control signal.

[Prior Art and its Problems J] A well-known amplitude side-limiting circuit introduces an alternating signal into the input terminal 3 of a differential amplifier 1, as shown in the block diagram of FIG.
The output signal is sent to terminal 18. After this output signal is converted into a DC signal by the detector 5, it is compared with the DC control signal applied to the terminal 22 by the error amplifier 7, and the gain of the differential amplifier 1 is controlled by M using this error signal. . As a result, the input alternating signal amplitude is controlled according to the magnitude of the DC control signal. In this case, the linearity of the detector 5 included in the feedback circuit directly affects the linearity of the entire amplitude control circuit. Furthermore, since the overall dynamic range is also limited by the detector, it is difficult to obtain a wide dynamic range. Furthermore, when the frequency of the human-powered police box signal is low, there is a drawback that the overall response speed is slow due to the detection time.

Also, unlike the above, in the case of an open loop that does not feed back the output signal, the dynamic range can be widened because a detector is not required, but linearity and stability generally change depending on the surrounding temperature and environment. There were drawbacks such as.

[Purpose of the invention]

It is an object of the present invention to provide an amplitude control circuit with a wide dynamic range and good linearity, while eliminating the above-mentioned drawbacks.

[Summary of the invention]

According to an embodiment of the present invention, the entire differential amplifier is inserted into a feedback circuit of an operational amplifier, and the collector current when the transistors constituting the differential amplifier are conductive is controlled by a DC or AC control signal. The amplitude of the alternating signal introduced into the input terminal of the differential amplifier is controlled by making it proportional to the magnitude. This will be explained in detail below using the drawings.

[Embodiments of the invention]

FIG. 1 is a block diagram of an amplitude control circuit according to an embodiment of the present invention. In the figure, a pair of transistors 11.1
3, whose base electrodes are respectively input terminals 12 for alternating signals.
．． 14 to constitute the differential amplifier 1. A load resistor 15,17 is connected to both collector electrodes, and the collector electrode of one transistor 13 is connected to an output terminal 18. Further, the inverting input terminal 24 of the operational amplifier 21 is connected to the input terminal 22 of the DC control signal Vc via the resistor 23, and at the same time is connected to the common connection point 16 of the load resistors 15 and 17. Further, the operational amplifier 2
The output terminal of transistor 1 is connected to both transistors 1 through resistor 25.
1.13 common emitter electrode.

The operation of the amplitude f+lI control circuit having the above-mentioned configuration will be explained with reference to the waveform diagram shown in FIG. before that,
In order to simplify the explanation, the following assumptions are made. (1) The current amplification factor (hf e) and high cutoff frequency (f T) of both transistors 11 and 13 are infinite, (2) the input impedance and gain of the operational amplifier 21 are infinite, and its output voltage (3) The load impedance connected to the output terminal 18 is infinite, and the resistances aiR1 and R4 of the load resistors 15 and 17 are equal. As a result, since the inverting input terminal 24 of the operational amplifier 21 is at the virtual ground point, the current I flowing through the resistor 23 (its resistance value is R3) becomes 1=V c /R3. This current directly becomes the collector current of the transistor 15 or 17 (see FIG. 2B). On the other hand, if the amplitude of the alternating signal introduced into the input terminal 12.14 is sufficiently large as shown in FIG. Repeat. As a result, a rectangular wave signal having an amplitude of Vc-R1/R3 is obtained at the output terminal 18 as shown in FIG. 2C. That is, the output voltage of this circuit becomes a rectangular wave signal whose frequency is equal to the input frequency of the alternating signal and whose peak-to-peak value is proportional to the DC control signal vc.

It should be noted that the circuit described above has a high signal frequency (e.g. 160 M
Hz), a neutralizing capacitor is connected between the base electrode of transistor 11 and the collector electrode of transistor 15 to offset the influence of the collector capacitance of transistor 15 in order to widen the dynamic range. Further, if a low-pass filter is inserted between the common connection point 16 and the inverting input terminal 24, the performance can be further improved. Further, in the above description, a DC signal was used as a control signal introduced into the operational amplifier, but this may be an alternating signal, and furthermore, a collector-emitter resistance of a transistor may be used instead of the resistor 25.

(Effects of the Invention) As detailed above, since the amplitude control circuit according to the present invention does not use a detector, a control circuit having a wide dynamic range, that is, from the high level to the low level of the input signal, can be obtained. In addition, the switching operation of the transistors that make up the differential amplifier is performed reliably, and the collector current when these transistors are turned on is precisely controlled by the operational amplifier, so the level of the output signal depends on the magnitude of the control signal. be exactly proportionate. Moreover, since this circuit does not have a factor that slows down the response like a wave detector, the response speed is fast for a wide range of signal frequencies. Further, the proportionality constant of the output signal level to the control signal is only two resistance values and does not include parameters that are easily affected by environmental changes such as temperature, so stability is good.

[Brief explanation of drawings]

FIG. 1 is a block diagram of an amplitude control circuit according to an embodiment of the present invention, FIGS. 2A to 2C are waveform diagrams of various parts thereof, and FIG. 3 is a block diagram showing a conventional circuit. 1. Differential amplifier, 5: Detector, 7: Error amplifier, 3.
12, 14: input terminal for alternating signal, 18: output terminal, 21: operational amplifier, 22: input terminal for control signal. , Applicant Yokotsutsu Hewlett Packard Co., Ltd. Agent Patent Attorney Tsuguo Hasegawa A 16-F; 3.2

Claims (1)

[Claims] In a differential amplifier consisting of a pair of transistors, an input alternating signal is introduced into both base electrodes to turn both transistors on and off alternately, and both collector electrodes are connected to the inverting input of the operational amplifier through resistors having the same resistance. a control signal is introduced through a resistor to the inverting input terminal, and the output signal of the operational amplifier is connected to the collector electrode of one transistor by commonly introducing it to the emitter electrode of both transistors. An amplitude control circuit characterized in that it takes out an alternating output signal.