JPH07263990A - Logarithmic amplifier - Google Patents

Abstract

PURPOSE:To provide the logarithmic amplifier which is equipped with a wide dynamic range and improves linearity. CONSTITUTION:An attenuator is inserted to one of two systems of an input signal, mutual signal levels are made different, and logarithmic transformation and A/D conversion is executed. A level switching point VL of both the signals is set by a reference voltage Vref. A switching signal 14 is outputted from an adder 7 near a saturation point based on the level switching point VL at a logarithmic amplifier (1)1 in a low level area. Corresponding to this signal 14, a hold circuit 8 holds the output signal of an A/ D converter (1)2, and the signal systems are switched to a logarithmic amplifier (2)5 by switchers (1)9 and (2)10. A synthesizer 11 synthesizes and outputs both the signals. The output signal is converted to an analog signal and outputted by a D/A converter 12. Since the signals at low and high levels are digitally synthetically joined, no synthetic distortion is generated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a logarithmic amplifier,
In particular, it relates to a logarithmic amplifier having a wide dynamic range.

[0002]

2. Description of the Related Art As shown in FIG. 4, a circuit example of a conventional logarithmic amplifying device includes a LOG (1) 301, an attenuator 302, and a LOG
(2) It comprises 303 and an analog synthesizer 304. In this logarithmic amplifier, LOG (1) 30
1 and LOG (2) 303 are logarithmic amplifiers having the same input-output characteristics. These two logarithmic amplifiers LOG (1) 3
The attenuator 302 is inserted into one of 01 and LOG (2) 303 to shift the operation start level with respect to the input signal level. By analog-synthesizing the outputs of these two logarithmic amplifiers to form one output, a wider dynamic range characteristic than that obtained by equivalently using one logarithmic amplifier is obtained.

In FIG. 5, in the low input level region, the combined log output voltage is dominated by the output of LOG (1), in the middle region of the input level, the output voltage of LOG (1) 301 reaches the saturation region, LOG (2) 303 instead
Output rises. L in the large area of input level
The output of OG (1) 301 is completely saturated, and this LOG (1) 3
The saturation voltage of 01 and the output voltage of LOG (2) 303 are combined and output.

As an example related to the above-mentioned prior art, the invention described in Japanese Patent Laid-Open No. 3-94521 discloses an output signal of 1 by n logarithmic amplifiers, 2 analog multiplexers and 2 A / D converters. And 1 control output.

[0005]

However, in the above-mentioned conventional logarithmic amplification device, since the signals amplified for each region are combined in analog, the generation of distortion cannot be prevented in the peripheral region of the combining point. At the combination switching point 401 in the middle area of the above figure, the saturation output of LOG (1) 301 and the rising output of LOG (2) 303 are combined, and therefore, synthetic distortion due to disturbance of both characteristics occurs. Further, variations in the gains of these two logarithmic amplifiers also cause synthetic distortion. In the conventional logarithmic amplification device by analog synthesis, the synthesis distortion occurs as described above, and it is difficult to improve the linearity.

It is an object of the present invention to solve the above conventional problems and provide a logarithmic amplifier having a wide dynamic range and excellent linearity.

[0007]

In order to achieve the above object, a logarithmic amplification device of the present invention converts a signal level of an input signal into a plurality of different levels, performs logarithmic amplification of each level, and outputs the amplified signal as one signal. A logarithmic amplification device for synthesizing and outputting to each other, A / D conversion means for converting each logarithmically amplified signal into a digital signal, and a digital signal converted by the A / D conversion means in order of magnitude of signal level And a synthesizing means for synthesizing based on the above.

Further, the synthesizing means has a holding means for storing the digital signal, the digital signal of the output signal of the logarithmic amplifying means having a lower signal level is stored by the holding means, and the logarithmic amplifying means is stored from the stored digital signal value. It is preferable that the output signal of the logarithmic amplifier having a signal level one step higher than the above is continuously combined.

Further, the logarithmic amplification device preferably has D / A conversion means and converts the output signal combined by the combining means into an analog signal.

[0010]

According to the logarithmic amplifier of the present invention, each of the logarithmically amplified signals is converted into a digital signal, and the A / D-converted digital signals are combined based on the order of the magnitude of the signal level. Therefore, the separately amplified signals can be made into one continuous signal, and a signal with excellent linearity can be obtained.

[0011]

Embodiments of the logarithmic amplification device according to the present invention will now be described in detail with reference to the accompanying drawings. Referring to FIG. 1, there is shown one embodiment of the logarithmic amplification device of the present invention.

FIG. 1 shows a system of a logarithmic amplifier according to an embodiment of the present invention as a circuit configuration block diagram, and FIG. 2 shows input-output characteristics of the logarithmic amplifier of FIG. Further, FIG. 3 shows another embodiment.

The embodiment of the logarithmic amplification device shown in FIG.
One amplification and digital signal conversion system, switching / combiner 3
And a D / A converter 12.

One amplification and digital signal conversion system is composed of a LOG (1) 1 and an A / D converter (1) 2 and amplifies an input signal in a low region. The other amplification and digital signal conversion system is composed of an attenuator 4, a LOG (2) 5 and an A / D converter (2) 6 and amplifies a large area input signal. LOG (1) 1 and L of these components
The OG (2) 5 is a logarithmic amplifier, and the A / D converter (1) 2 and the A / D converter (2) 6 are signal converters from analog signals to digital signals. The attenuator 4 is a circuit unit that reduces the signal level of the analog input signal, and is generally composed of a resistor having good temperature characteristics.

The switching / combining unit 3 is a circuit section which converts the above-mentioned two digital signals into one system signal. For this purpose, it has two input signal terminals, an input terminal for adding a predetermined reference value Vref13 to one input signal, and an output terminal for one signal. One input signal terminal of the switching / combining device 3 is connected to the input terminal of the hold circuit 8 and the switching device (1).
9 is connected to one input terminal, and the output terminal of the hold circuit 8 is connected to the other input terminal of the switch (1) 9.

The other input signal terminal of the switch / combiner 3 is connected to one input terminal of the adder 7. The input terminal for inputting the reference value Vref13 is connected to the other input terminal of the adder 7. The signal terminal of the output data of the adder 7 is connected to one input terminal of the switch (2) 10. Further, the adder 7 outputs a flag when the output value of the data to be added becomes a predetermined value or more. This output signal is used as the switching signal 14, and the hold circuit 8 and the switching device (1)
9 and the control terminal of the switch (2) 10. A signal of “0” potential value is input to the other input terminal of the switch (2) 10.

A switch which is a 2-input 1-output line switch
The output terminals of (1) 9 and the switch (2) 10 are connected to the input terminals of the combiner 11, and the output terminals of the combiner 11 are connected to the output terminals of the switch / combiner 3. Switching / combiner 3
The output terminal of is connected to the digital signal input terminal of the D / A converter 12. The analog output signal of the D / A converter 12 is used as the output signal of the logarithmic amplifier.

In the switching / combining unit 3 composed of the above-mentioned respective circuit parts, the hold circuit 8 is a temporary storage circuit for digital signals and is composed of, for example, a RAM. The holding timing is performed based on the switching signal 14 output from the adder 7, and the held digital signal is output to one signal input terminal of the switching device 9. The switch 9 is
The hold signal output from the hold circuit 8 and the non-hold real signal are selectively switched to output any one of the signals.

The adder 7 shifts the level of the logarithmically amplified signal in the large area, compares it with a predetermined value, and outputs the switching signal 1
4 is a circuit unit that outputs 4. The reference voltage Vref13 is input to perform this shift and comparison. When the large-area logarithmic amplified signal input to the adder 7 reaches the reference voltage Vref, the switching signal 14 is output as a flag. This flag is connected in parallel between the hold timing input terminal of the hold circuit 8 and the switching drive terminals of the switch (1) 9 and the switch (2) 10. Therefore, the hold circuit 8,
The switch (1) 9 and the switch (2) 10 operate at the same timing.

Next, the input-output characteristics of the logarithmic amplifier of this embodiment will be described with reference to FIG.

In each of the waveforms of FIG. 2, the waveform 111 shown by the alternate long and short dash line is LOG (1) 1, the waveform 112 shown by the dotted line is LOG (2) 5, and the waveform 11 shown by the solid line is D / A converter 1.
2 is each output waveform.

In the symbols in FIG. 2, the symbol VH is the voltage value at the junction of the composite waveform 11, and the symbol VL is the voltage value whose negative value is applied as the reference voltage Vref13.
The symbol VL is the voltage value of the waveform 112 in the large region at the input level of the junction point VH. The symbol VH is set near the upper limit having the linearity of the logarithmically amplified waveform 111 in the low region. At this point, the large area logarithmic amplified signal 112
Is joined with.

The interval L between the waveforms 111 and 112 is
This is the level difference between the signals of the two systems by the attenuator 4. Symbol V
H is a switching junction point of the two waveforms 111 and 112, and corresponds to a numerical value stored in the hold circuit 8. The symbol D1 is the dynamic range of the logarithmic amplifier of 1, and the symbol D2 corresponds to the increase of the dynamic range increased by the amplification of the two systems.

1 and 2, the reference voltage Vref1
3 is near the upper limit of the linear region of the waveform 111 in the low region (V
H) is set to a negative value (-VL) at the point (VL) of the large-area waveform 112. In the switching signal 14 of the adder 7, the level is low at a level lower than the point (VL) in the large area, and becomes high when the point (VL) is reached. This switching signal 14 switches between the low and large region signals entering the combiner 11. Also, at this switching point, the output value of the addition data of the adder 7 is "0", and the subsequent rising data B is the hold circuit 8 in the low region.
Is added and combined with the signal A held by. This relationship will be described in detail below.

The input level is the switching point (VH / VL) in FIG.
When it is lower, the output of the A / D converter (1) 2 is the switch (1) 9
To the input A of the synthesizer 11. The "0" voltage from the switching device (2) 10 is applied to the input B of the combiner 11 at this time. Therefore, the output value of the A / D converter (1) 2 is directly output to the D / A 12.

When the input level exceeds the value of "middle" in FIG. 2, the output of the A / D converter (2) 6 is the reference voltage (VH / VL).
And the switching signal 14 is turned on. At this time, the hold circuit 8 operates to hold the output (VH) of the A / D converter (1) 2. Further, the switch (1) 9 and the switch (2) 10 are operated, and the combiner 11 combines the output (VH) of the hold circuit 8 and the data from the adder 7 and outputs it to the D / A 12.

The D / A 12 receives the digital output value from the synthesizer 11, converts it into an analog value, and outputs it. The output signal from the D / A 12 based on the above procedure does not cause waveform distortion and distortion at the junction because the junction between the two systems of signals is digitally switched and combined.

FIG. 3 is a circuit block diagram showing another embodiment of the present invention. In this embodiment, an amplifier 15 is inserted in front of the logarithmic amplifier 1 for one analog signal in order to make the signal levels of the two systems different. This amplifier 15
Serves as an alternative to the attenuator 4 of the embodiment of FIG. By adopting an amplifier for this attenuation, the gain of the signal in the logarithmic amplifier can be gained. The other operations are the same as those in the above embodiment.

As described above, according to the present invention, since the level-shifted logarithmic amplifier outputs are digitally combined in a range with good linearity, a logarithmic amplifier having a wide dynamic range and excellent linearity can be provided. can get.
Further, since the two logarithmic amplifier outputs are digitally combined, no adjustment of the switching / combining circuit 3 is necessary, and the IC
A logarithmic amplifier having good characteristics can be obtained easily at low cost and easily integrated (integrated circuit).

Although the above-described embodiment is a preferred embodiment of the present invention, the present invention is not limited to this, and various modifications can be made without departing from the gist of the present invention. For example, in the above embodiment, switching / combining is performed in two stages, but the number of stages is not limited to two. Further, although the A / D converter is provided at each stage of the signal amplification system, it is also possible to switch the analog signal system and configure one A / D converter.

[0031]

As is apparent from the above description, the logarithmic amplification device of the present invention converts each logarithmically amplified signal into a digital signal, and the A / D-converted digital signal is converted into a signal having a signal level magnitude. It is possible to combine the signals based on the ranks and separately amplify the signals into one continuous signal. Since this synthesis is performed on the digital signal, it is possible to perform synthesis without distortion in the synthesis unit and without distortion.

[Brief description of drawings]

FIG. 1 is a circuit configuration block diagram showing an embodiment of a logarithmic amplification device of the present invention.

FIG. 2 is a graph showing input-output characteristics of the device of FIG.

FIG. 3 is a circuit configuration block diagram showing another embodiment of the logarithmic amplification device of the present invention.

FIG. 4 is a block diagram showing a circuit configuration example of a conventional logarithmic amplifier.

5A and 5B are graphs for explaining an example of characteristics of the apparatus of FIG. 4, in which FIG. 5A shows input-output characteristics before and after combining.

[Explanation of symbols]

 1 Logarithmic Amplifier 2 A / D Converter 3 Switching / Combining Circuit 4 Attenuator 5 Logarithmic Amplifier 6 A / D Converter 7 Adder 8 Hold Circuit 9 Switcher 10 Switcher 11 Combiner 12 D / A Converter 13 Reference Voltage 14 Switching signal 15 Amplifier

Claims (3)

[Claims] 1. A logarithmic amplification device for converting a signal level of an input signal into a plurality of different levels, logarithmically amplifying the respective signals, synthesizing the amplified signals into a single signal, and outputting the combined signal. An A / D conversion means for converting into a digital signal, and a synthesizing means for synthesizing the digital signal converted by the A / D conversion means based on the order of the magnitude of the signal level. Logarithmic amplifier. 2. The synthesizing means has a holding means for storing the digital signal, the digital signal of an output signal of the logarithmic amplifying means at a lower level of the signal level is stored by the holding means, and the stored 2. The logarithmic amplification apparatus according to claim 1, wherein the synthesis is continuously performed from a digital signal value to an output signal of the logarithmic amplifier having the signal level one step higher than the logarithmic amplification means. 3. The logarithmic amplification device according to claim 1, wherein the logarithmic amplification device further has D / A conversion means, and converts the output signal synthesized by the synthesis means into an analog signal. apparatus.