JPS58143617A - Logarithmic amplifying circuit - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION When measuring the received electric field strength, the present invention makes the output voltage change linearly in response to logarithmic voltage fluctuations in the input level (Secondly, the wide level fluctuation range of the received electric field strength is measured). This invention relates to an improvement of a logarithmic amplifier circuit that enables detection.

First, a conventional logarithmic amplifier circuit will be explained. FIG. 1 is a block diagram of an example of a circuit configuration, and a logarithmic amplifier circuit is provided in an intermediate frequency amplification section of a field strength measuring device or a receiver. In the figure, 1 is intermediate frequency input, 2 is intermediate frequency output, 8 is logarithmically amplified output, 4 to 1
1 is each stage of intermediate frequency amplification, 12.18 is an adder, 14
is a wave detector.The output of each stage of amplifiers 1, 4 to 11 is in phase with the input, and the voltage divided by the output resistance and the adder input resistance of 12.18 is applied to the adder 12.18. becomes the output voltage. The adders 12 and 18 obtain a logarithmically amplified output 8 by performing envelope detection with the detector 14 through a buffer amplifier so that mutual influence is reduced.

However, in such a circuit, (1) the phase from the first stage to the last stage of the intermediate frequency amplifier must be the same;
Phase correction at the intermediate frequency used becomes complicated. (2)
If the amplification gain from the first stage to the final stage is large, there are drawbacks such as the need to increase the isolation of the buffer amplifier to prevent oscillation.

The present invention was developed to eliminate these drawbacks, and is characterized by the fact that instead of adding intermediate frequencies, DC voltages are added, thereby making it easier to perform phase correction and prevent oscillation. , will be explained in more detail below.

FIG. 2 is a diagram showing an example of the configuration of a logarithmic amplifier circuit embodying the present invention.
1 to 11 are the same as in FIG. 1, 12-1.12-2 is an adder, 14-1.14-2 is a detector, and 15 is an adder. In the present invention, first, the intermediate frequency section of a receiver or measuring instrument is divided into a front amplifier group consisting of 4 to 7 in this example and a rear amplifier group consisting of 8 to 11, and a portion of the output voltage of each stage amplifier of each amplifier group is divided. are taken out from each stage in the same phase, added by a common load resistance for each group (not shown), and then detected, and the outputs of the logarithmic amplifiers of each amplifier group, which become DC outputs, are added by a DC adder 15. This is set as the logarithmic amplifier output 8 for the input 1 of the intermediate frequency section, and at the same time, the output of the final stage 11 of the rear amplifier group is set as the output 2 to the receiver demodulator.

The input/output phase difference of each of the amplifiers 4 to 7 in the amplifier group is corrected using a capacitor, etc., and the phase difference between the input signal l and the output of amplifier 7 is made as small as possible by making the phase difference as small as possible. The output is added to the input resistance of adder 12-1 by resistance division, and the output of adder 12-1 is subjected to envelope detection by detector 14-1, which combines the logarithmic characteristics of each amplifier. 11 with wide dynamic range
The logarithmic amplifier output is obtained. Amplifiers 8 to 11 belonging to the rear amplifier group are also exactly the same as the front amplifier group, and phase correction is performed at each stage, and the output synthesized by the adder 12-2 is sent to the detector 14-2.
2, a second logarithmic amplifier output with a wide dynamic range can be obtained. Subsequently, each detector 14-
By combining the DC outputs from 1 and 14-2 by an adder 15, a logarithmic amplifier output 8 with a wide dynamic range is obtained.

Now, if the phase difference of each amplifier in FIG. 2 is set to θ (ideally zero), the combined amplitude will be as follows.

As θ increases, the amplitude decreases, and the linearity of the logarithmic amplification characteristics worsens. However, even if θ is large, if n is small, the second term (sin term) in the above equation can be ignored, so the linearity of the logarithmic amplification characteristic is not significantly impaired. When something with such characteristics is detected, the intra-group phase difference of the front amplifier group and the intra-group phase difference of the rear amplifier group are essentially the same for each detector output, and the detected output of the input l and the amplifier, for example 7, is the same. The phase difference between is not related to the detection output. In other words, there is no phase term in the outputs of the detectors 14-1 and 14-2, and even if they are DC-combined by the adder 15, the result is a sum of only the amplitude components of 14-1 and 14-2, which has good linearity. A logarithmically amplified output of 8 is obtained. Furthermore, since the front and rear amplifier groups have a small phase difference between their inputs and outputs and have a small amplification gain which is divided into two, they are less likely to satisfy oscillation conditions and are useful in preventing oscillation.

As described in detail above, in the present invention, since the output amount phase difference between each amplifier group is small, oscillation is difficult to occur and the characteristics are stable without variation.

Furthermore, since the logarithmic amplification characteristics of each amplifier are combined, logarithmic amplification with a wide dynamic range is performed and a stable detection output with good linearity can be obtained, which is a significant practical effect.

[Brief explanation of the drawing]

FIG. 1 is a configuration example diagram of a conventional logarithmic amplifier circuit, and FIG. 2 is a configuration example diagram of a logarithmic amplifier circuit embodying the present invention. ■・・・Intermediate frequency input, 2・・・Intermediate frequency output,
8... Logarithmic amplification output, 4-11... Intermediate frequency amplifier at each stage, 12, 12-
1.12-2.13... Adder, 14.14-1.
14-2...Detector, 15...Adder. Patent applicant Kokusai Denki Co., Ltd. agent Okyu 1 person from outside the university

Claims (1)

[Claims] A multi-stage amplification intermediate frequency amplification circuit is used as a circuit to obtain a logarithmically related output for an intermediate frequency input, and all stages are divided into a front amplifier group and a rear amplifier group (a part of the output of each stage amplifier is sent from each stage). are taken out in the same phase, added together using a common resistor provided for each amplifier group, and then detected. The extracted logarithmically amplified outputs of each amplifier group are added in direct current using an adder, and this is added to the intermediate frequency signal. A logarithmic amplifier circuit configured to provide a logarithmic output with respect to an input.