JPH0325182Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to a level measuring circuit equipped with a DC comparator that compares a DC signal obtained by rectifying an AC signal with a reference voltage.

Figure 1 shows an automatic gain adjustment amplifier circuit of a measuring instrument to which this invention can be applied, where T ₁ is the input terminal of the signal under test, T ₂ is the output signal of the level meter,
10 is a Batsha amplifier, 20 is a DC comparator 14
The variable attenuator is controlled by the output voltage of the light emitting diode 18 and the photoconductive element 19. 30 is a voltage amplifier whose gain is controlled by the variable attenuator 20, and 40 is a feedback circuit, which is composed of a full-wave rectifier 11, a smoothing circuit 12, a low-pass filter 13, and a DC comparator 14. Note that 15 is a lock switch, 16 is a sample and hold circuit, and 17 is a reference voltage source.

This measuring circuit is used to compare two signals and read the difference in measuring sound pressure levels, S/N ratios, etc., and its operation will be briefly explained below.

First, the first signal to be measured is inputted from the input terminal _T1 , and the output of the amplifier 30 at that time is read at the output terminal _T2 of the level meter. This output voltage is full-wave rectified in a feedback circuit 40 and further smoothed to a voltage corresponding to the peak value of the AC signal, which is then compared with a reference voltage source 17 in a DC comparator 14. Since the output of the DC comparator 14 is a so-called loop control circuit that controls the variable attenuator 20, the input voltage is the same as that of the reference voltage source 1.
7 makes the output voltage constant. Therefore, this constant voltage is set to 0 [db], the output voltage of the low-pass filter 13 at that time is stored in the sample and hold circuit 16, and the lock switch 15 is opened. When the second voltage to be measured is input to input terminal T ₁ in this state, that is, with loop control released, the swing of the level meter at output terminal T ₂ will be different from the previous voltage to be measured. Since it shows the amplitude value corresponding to the difference, the difference between two signals can be measured by directly connecting a level meter.

By the way, if the output of the low-pass filter 13, which becomes the input signal of the DC comparator 14, is not made into a complete DC voltage, for example, if ripple is included, the ripple component will also be detected in the output of the DC comparator 14, so the overall This may cause abnormal behavior. Therefore, the configuration of the low-pass filter 13 requires a multi-stage and fairly complicated circuit.

This idea was made in consideration of these points, and by improving the DC comparator, the accuracy of the level measurement circuit can be improved so that a comparison output that is unaffected by ripple components can be obtained even for DC voltages that include ripple components. This makes it possible to simplify the circuit without reducing the performance. Figure 2 shows a DC comparator improved with this invention, where 21 is a full-wave rectifier;
22 is a smoothing circuit, 23 is a DC comparator, and 24 is a reference voltage source. This circuit shows the main configuration of the feedback circuit 40 of the measurement circuit shown in FIG. A capacitor is used as a wave circuit from the output terminal 23c to the inverting input terminal 23a.
C ₀ is connected.

This DC comparator 23 can output the potential difference between the DC voltage input to the non-inverting input terminal 23b and the reference voltage source 24 with a high gain, and also outputs the potential difference between the DC voltage input to the non-inverting input terminal 23b and the reference voltage source ₂₄ with a high gain. Therefore, even if there is some ripple component in the DC component input to the non-inverting input terminal 23b, the reference value for the ripple component is The voltage difference between the voltage source 24 and the voltage source 24 is almost never output.

Therefore, by using such a DC comparator 23 in a level measuring circuit, the low-pass filter 13 shown in FIG. 1 can be omitted. Furthermore, even when the low-pass filter 13 is provided, a DC comparator with higher accuracy (not affected by ripple components) can be realized.

Figure 3 shows a gain control resistor in the DC comparator 23.
This shows a specific example in which the operation is made more stable by adding R _s and R _f , and the difference between the voltage of the reference voltage source 24 and the DC voltage of the smoothing circuit 22 is multiplied by 1 + R _f /R _s s in the comparison output. The comparison output of the ripple component is almost never outputted by the capacitor _C0 .

As explained above, the level measuring circuit of this invention has a low-pass filter function in the high gain circuit that constitutes the DC comparator, so it will not malfunction even if there is a ripple component in the DC voltage to be compared. The level measuring circuit can be constructed at a lower cost.

[Brief explanation of the drawing]

Fig. 1 is a block diagram of a measurement circuit to which this invention can be applied, Fig. 2 is a block diagram showing an example of a DC comparator adopted in this invention, and Fig. 3 is a block diagram of a DC comparator adopted in this invention. FIG. 7 is a circuit diagram showing another embodiment of the comparator. In the figure, 21 shows a full-wave rectifier, 22 shows a smoothing circuit, 23 shows a DC comparator, and 24 shows a reference voltage source.

Claims (1)

[Scope of utility model registration request] The input signal to be measured is supplied to an amplifier via a variable attenuator, the output signal from this amplifier is supplied to a level meter, and a DC voltage obtained by rectifying and smoothing a part of the output signal of the amplifier is supplied to a DC comparator. In the level measuring circuit, the DC comparator has a non-inverting side output level. The DC voltage is supplied to one input terminal, the reference voltage is connected to the second input terminal on the inverting side, and the output of this DC comparator is connected to the second input terminal via a capacitor. A level measurement circuit comprising an amplifier.