JPS6151806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a logarithmic amplifier device that is applied to, for example, a spectrum analyzer, a selective level meter, etc., and whose input/output characteristics are logarithmic characteristics.

For example, as shown in FIG. 1, a high frequency signal from an input terminal 11 is amplified by a logarithmic amplifier 12, detected by a detector 13, and displayed on a display 14 to logarithmically display the level of the high frequency signal. ing. In this case, the input signal of input terminal 11 is
At 0 dBm, the output of the detector 13 is 5 V, and the high frequency signal is -10 dBm, -20 dBm, -30 dBm, ... -90 dBm, -
At 100dBm, the output of the detector 13 is 4.5V,
The input/output characteristics of the logarithmic amplifier 12 change logarithmically so that when the level of the high-frequency signal changes logarithmically such as 4V, 3.5V, ...0.5V, 0V, the output of the detector 13 changes linearly. It is configured as shown. However, in reality, it has been difficult to obtain something that exhibits such accurate logarithmic characteristics.

An object of the present invention is to provide a logarithmic amplifier that exhibits ideal logarithmic characteristics.

According to this invention, the error in the input/output characteristics of the logarithmic amplifier used is calculated, stored in a memory, and the error corresponding to the input signal is read out from the memory, corrected, and sent out as a correct output. do.

For example, in FIG. 2, corresponding parts to those in FIG. The amplified signal from the input terminal 11 or the standard signal from the oscillator 16 is selectively inputted to the variable level adjuster 15 using a changeover switch 17, and the level thereof is adjusted and output.For example, a variable attenuator or a variable A gain amplifier is used. As an example
A variable attenuator is used that can vary up to 100 dB in 1 dB steps. The output of this variable level adjuster 15 is supplied to a logarithmic amplifier 12. This amplified output is detected by a wave detector 13 and converted into a digital signal by an AD converter 18.

The digital signal from this AD converter 18 is supplied to a calculation section 19 that performs error calculation and correction calculation. The calculation unit 19 calculates the error of the logarithmic amplifier 12 when the standard signal is supplied to the level adjuster 15, stores the calculation result in the memory 21, and also calculates the error when the amplified signal is applied to the level adjuster 15. A correction operation is performed on the output of the AD converter 18 in , and the correction operation result is supplied to the DA converter 22 to be converted into an analog signal to obtain a target amplified output. This amplified output is displayed on display 1 as necessary.
4.

As described above, the calculation section 19 inputs the standard signal from the oscillator 16, calculates the error in the input/output characteristics of the logarithmic amplifier 12, and stores the error in the memory 21. For this purpose, a so-called microcomputer is used in this example. The CPU 23 of the microcomputer reads out the program in the program memory 24, decodes and executes it, and outputs the program to the level adjuster 15 through the output port 25.
At that time, the standard signal from the oscillator 16 is, for example, 0 dBm, and the level adjuster 15 is set.
At that time, the AD converter 18 converts the digital signal into the CPU 23 through the input port 26, and the amplifier 12 outputs the signal from the input digital signal, the set level of the level adjuster 15, and the standard signal level. Calculate the error with respect to the ideal value of the input/output characteristics. The calculation result is stored in memory 2.
Remember it in 1. In this way, the level adjuster 15 is made into a variable attenuator, and the attenuation is set to 0.
Each error with respect to the ideal value is stored in the memory 21 corresponding to each output of the amplifier 12 when the amount of attenuation is increased by 1 dB.

When amplifying the signal to be amplified from the input terminal 11, it is made to pass through the level adjuster 15 as is, that is, the input signal is passed through without level adjustment, and the conversion output of the AD converter 18 at that time is CPU 23 through input/output port 26
, reads out the error signal corresponding to the digital value to the memory 21, performs addition and subtraction on it, that is, performs a correction operation, and supplies the result of the operation from the output port 25 to the AD converter 22,
Therefore, an ideal output signal is extracted from the DA converter 22.

Incidentally, when the level adjuster 15 amplifies the signal from the input terminal 11, it is set to an appropriate value according to the level of the input signal, and it is not necessarily necessary to pass the signal as is. Furthermore, in general, in such a device, the error, that is, the error of the logarithmic amplifier 12, often changes due to the influence of the ambient temperature.
Therefore, if the error calculation is performed periodically or every time the signal to be amplified is input, an accurate logarithmically amplified output can always be obtained. In order to automatically perform the error calculation in this way, that is, to perform the error calculation automatically periodically or each time this device is used, it is necessary to write the storage program in the program memory 24 in such a manner. This can be done by In order to obtain the required accuracy, the AD converter 18 may output approximately 10 bits.

As described above, according to the logarithmic amplifier according to the present invention, even if the input/output characteristics of the logarithmic amplifier 12 are not ideal, it is possible to obtain an output similar to that when the input/output characteristics of the logarithmic amplifier 12 are ideal. Even when changes occur due to the influence of temperature, the influence can be eliminated and correct output can be obtained. This device can be used not only as a spectrum analyzer, but also for example as a selective level meter, and in addition to such measurements, it can also be used generally for amplifying and detecting input high frequency signals.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional logarithmic amplifier, and FIG. 2 is a block diagram showing an example of a logarithmic amplifier according to the present invention. 11: Input terminal, 12: Logarithmic amplifier, 13: Detector, 14: Display, 15: Variable level adjuster,
16: Standard signal oscillator, 18: AD converter, 1
9: Arithmetic unit, 21: Memory for storing error signals,
22: DA converter.

Claims (1)

[Claims] 1. A variable level adjuster to which an input signal is supplied and whose level can be changed; a logarithmic amplifier with logarithmic input/output characteristics for amplifying the level-adjusted output; and a detector for detecting the amplified output. , A- which converts the detection output into a digital signal.
A D converter and its digital signal are input, and the logarithmic amplification characteristic error of the logarithmic amplifier is calculated from the setting value of the level adjuster, the standard signal level, and the input digital signal, and when the input to be amplified is added. Correcting calculation means for performing a correction calculation from the digital signal and its corresponding error from the corresponding AD converter; an error memory for storing the error obtained by the above error calculation; and an error memory for storing the error obtained by the above error calculation; Perform calculations on analog signals to obtain logarithmically amplified output
A logarithmic amplifier equipped with a DA converter.