JPH0718179Y2 - Automatic gain adjustment circuit - Google Patents

Description

[Detailed description of the device]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an automatic gain adjustment circuit for performing automatic gain control in a reception amplification circuit for receiving a signal which is intermittently transmitted like a burst wave signal such as an ultrasonic wave.

[0002]

2. Description of the Related Art As a conventional automatic gain adjustment circuit, there is one using a hold circuit as shown in FIG. In FIG. 3, since the sample hold circuit 15 cannot hold data for a long time, its output has a small value.
Therefore, since the division circuit 16 divides the input signal Vi by a small value, its output becomes large, and the division circuit 16 operates as a high gain amplifier.

At this time, when the burst wave signal is input to the division circuit 16 as the input signal Vi, its output becomes larger than the specified value, and the output of the detection circuit 12 and the multiplication circuit 13 using one input as the reference voltage Ri. The output of is also large. The comparator 14 samples the input value to the sample hold circuit 15, and when the comparator 14 detects the burst wave signal, the output of the sample hold circuit 15 becomes large.

In this state, for the first time, the division circuit 16 operates so as to reduce the amplification degree, and the output signal Vo is controlled from excessive output to proper output.

[0005]

However, in the above-mentioned conventional automatic gain adjustment circuit, the sample hold circuit 15 can hold the data only for a limited time, and therefore, until the next burst wave signal is input. To the initial state, that is, the output value is small. FIG. 4 shows a waveform chart of each part in the above operation.

Therefore, particularly in the case of a long-period burst wave signal in which the burst wave signal rarely appears, the detection signal cannot be correctly held until the next burst wave signal appears in the sample hold circuit 15, and the automatic gain adjustment circuit. It was difficult to operate properly.

Another conventional example is an automatic gain adjustment circuit that incorporates a microprocessor (CPU) and controls by digital processing. In FIG. 5, the input signal Vi
The burst wave signal inputted as is divided by the division circuit 21 by the output of the D / A converter 27 at that time, that is, the gain is controlled and output as the output signal Vo.

When the comparator 25 detects the output signal Vo, it outputs an interrupt signal to the CPU 24. As a result, the CPU 24 inputs the output of the A / D converter 22 via the interface circuit 23 and performs arithmetic processing so that the output of the A / D converter 22 becomes an appropriate value.
The arithmetically processed signal is output to the D / A converter 27 via the interface circuit 26. The signal D / A converted by the D / A converter 27 is input to the division circuit 21, and the output of the division circuit 21, that is, the output signal Vo is controlled from an excessive output to an appropriate output.

However, when the CPU is incorporated in the automatic gain adjustment circuit, software is required, and the circuit is complicated and expensive.

In view of the above problems, the present invention aims to provide an automatic gain adjustment circuit capable of accurately performing automatic gain control for an intermittent signal such as a burst wave signal regardless of the length of the intermittent period. And

[0011]

In order to achieve the above object, the present invention provides an automatic gain adjusting circuit for receiving a signal transmitted intermittently such as a burst wave signal and automatically controlling the gain of the received signal. A variable amplification means comprising a feedback circuit composed of a ladder resistance type D / A converter for inputting a detection signal and a ladder resistance type D / A converter, and an operational amplification circuit for gain control of an input signal, the output of the detection circuit and D /
An adder circuit for adding the output of the latch circuit input through the A converter and the inverting amplifier circuit, and an A / D converter and an A / D converter for analog-digital conversion of the output of the adder circuit
Detection signal generating means including a latch circuit that holds the output of the converter and outputs a detection signal to the D / A converter and the ladder resistance type D / A converter, and controls the A / D converter and the latch circuit by detecting the output signal. And a comparator that

[0012]

1 is a circuit diagram of an automatic gain adjusting circuit showing an embodiment of the present invention. In FIG. 1, the input signal Vi is input to one terminal of the operational amplifier circuit 11 of the variable amplifier circuit 1,
The gain is controlled and output as the output signal Vo. That is, the output signal Vo is the ladder resistance type D / A converter 10
Is fed back to the operational amplifier circuit 11 via the
The output signal Vo is controlled by the output voltage of the / A converter 10.

Here, the ladder resistance type D / A converter is
The voltage input to the reference voltage terminal is attenuated and output according to the voltage input to the control terminal. Ladder resistance type D
The output voltage of the / A converter 10 is controlled by the voltage value of the input signal Vi, that is, the output of the latch circuit 6.

The input signal Vi is detected by the detection circuit 2 and input to the addition circuit 4. The output of the adder circuit 4 is A / D converted by the A / D converter 5 and input to the latch circuit 6. The output of the latch circuit 6 is held until the next input signal Vi is input.

In the adder circuit 4, the previous input value held in the latch circuit 6 is added to the D / A converter 7 and the inverting amplifier circuit 3.
Is input to one of the input terminals via to obtain the difference between the current input value and the previous input value. When the output of the latch circuit 6 is smaller than the specified value due to the burst wave signal input last time, the output of the addition circuit 4 becomes higher than the previous value. Conversely, when the output of the latch circuit 6 is larger than the specified value, the output of the adder circuit 4 becomes smaller than the previous value.

As described above, the output of the latch circuit 6 allows the variable amplification circuit 1 to increase the amplification degree when the input signal Vi is smaller than the specified value, and conversely, when the input signal Vi is larger than the specified value. Operates to lower. As a result, the output signal Vo is automatically controlled to the optimum value.

The A / D converter 5 and the latch circuit 6 are controlled by the comparator 8, and the output of the adder circuit 4 is held in the latch circuit 6 only when the comparator 8 detects the burst wave signal. The detection signal can be correctly held until the burst wave signal is input, and new automatic gain control is performed only when the burst wave signal is input.

Next, the above operation will be analyzed. Figure 1
, The amplification degree G of the variable amplifier 1, the conversion constant K of the detection circuit 2, the output Vk of the detection circuit 2, the amplification degree -m of the inverting amplification circuit 3, the output Vm of the inverting amplification circuit 3, the output Va of the addition circuit 4, When the reference voltage Vr of the A / D converter 5, the output n of the A / D converter 5, the output N at the maximum input of the A / D converter 5, and the reference voltage Vr of the latch circuit 6 are set, the following relational expression is applied to each input. Is established.

Vo = G · Vi (1) Vk = K · Vi (2) Vm = Vr · (n / N) · (−m) (3) Va = Vk−Vm (4) G = N / n ( 5) n = (Va / Vr) * N (6) From the expressions (3) and (6), Vm = (-m) * Va (7) From the expressions (2) and (7), the expression (4) is Va = Vi · {K / (1-m)} (8) From Equation (5), Equation (6), and Equation (8), Equation (1) is Vo = (Vr / Va) · Vi = Vr · {( 1-m) / K} (9)

Equation (9) shows that the input signal Vi is controlled to a constant value as the output signal Vo by the automatic gain adjustment circuit of the present invention and is output. Furthermore, equation (9) is A
It is shown that the A / D converter 5 and the latch circuit 6 are controlled by the reference voltage Vr of the A / D converter 5 and the latch circuit 6, and the A / D converter 5 and the latch circuit 6 are controlled by the comparator 8 that detects the input of the burst wave signal. It is shown that new gain control is performed and output as the output signal Vo only when the burst wave signal is input as the input signal Vi.

FIG. 2 shows the construction of an automatic gain adjustment circuit according to another embodiment. The A / D converter 7 of FIG. 1 is replaced with a sample hold circuit 7 ', and the variable amplifier circuit 1 is replaced with a ladder resistance type D.
The A / A converter 10 alone is used.

In FIG. 2, since the input signal Vi is input to the reference voltage terminal of the ladder resistance type D / A converter 10 and is output as the output signal Vo from the output terminal, the variable amplifier circuit 1'operates as an attenuator. The sample hold circuit 7'holds the output of the adder circuit 4 in the burst wave signal input last time.
When the comparator 8 detects the burst wave signal, the comparator 8 outputs it to the inverting amplifier circuit 3. The circuit operation in FIG. 2 is similar to that in FIG. This circuit is effective when the input signal level is sufficiently high.

Although the ladder resistance type D / A converter 10 is used for the variable amplifier circuit 1 in the above embodiment, an equivalent circuit may be constituted by a resistor and a relay or an analog switch.

[0024]

As can be understood from the above description, the automatic gain adjustment circuit of the present invention can correctly hold the detection signal until the next burst wave signal is input. The advantage is that automatic gain control can be accurately performed regardless of the length of the intermittent cycle.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a configuration of an embodiment of an automatic gain adjustment circuit of the present invention.

FIG. 2 is a circuit diagram showing a configuration of another embodiment of the present invention.

FIG. 3 is a circuit diagram showing an automatic gain adjustment circuit using a conventional sample hold circuit.

FIG. 4 is a waveform chart in each part in FIG.

FIG. 5 is a circuit diagram showing an automatic gain adjustment circuit using a conventional microprocessor.

[Explanation of symbols]

 1, 1'Variable amplification circuit 2 Detection circuit 3 Inversion amplification circuit 4 Addition circuit 5 A / D converter 6 Latch circuit 7 D / A converter 7'Sample hold circuit 8 Comparator 10 Ladder resistance D / A converter 11 Operational amplification circuit

Claims (2)

[Scope of utility model registration request] 1. A ladder resistance type D / A converter for inputting a detection signal in an automatic gain adjustment circuit for receiving a signal transmitted intermittently such as a burst wave signal and automatically controlling the gain of the received signal, and A variable amplification means composed of an operational amplification circuit that constitutes a feedback circuit by a ladder resistance type D / A converter and controls the gain of an input signal, and a latch circuit that receives the output of the detection circuit and the D / A converter and the inverting amplification circuit. An adder circuit for adding the output, an A / D converter for analog-digital converting the output of the adder circuit, and an output for the A / D converter, which holds the output of the A / D converter and the ladder resistor type D / A converter. Detection signal generating means including a latch circuit for outputting a detection signal, and detecting the output signal to control the A / D converter and the latch circuit An automatic gain adjustment circuit comprising: a comparator. 2. The sample according to claim 1, wherein the variable amplification means is composed only of a ladder resistance type D / A converter, and the output of the adder circuit is input instead of the D / A converter in the detection signal generation means. A hold circuit, wherein the comparator controls the A / D converter and the sample and hold circuit.