JP2773628B2 - RMS detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an effective value detection circuit,
In particular, the present invention relates to an effective value detection circuit used for measuring a distortion factor of an audio D / A converter.

[0002]

2. Description of the Related Art A conventional effective value detection circuit of this type has an audio D / D converter as shown in FIG.
An analog input signal 101 output from the A converter is received, and an effective value detector 31 for detecting the effective value of the analog input signal 101 and a detection output 102 of the effective value detector 31 are input and integrated, and the detection is performed. A resistor 32 for suppressing a ripple included in the output and outputting a predetermined effective value detection signal 103
And a low-pass filter including a capacitor 33. Although the internal configuration of the effective value detector 31 is not shown in FIG. 3, as is well known, the effective value detector 31 is formed by a square detection integrated circuit including a multiplication circuit and a first-order low-pass filter. The low-pass filter included in the conventional example is called a secondary low-pass filter corresponding to the primary low-pass filter. This is the same in the following description.

In this type of conventional example, when used for measuring the distortion factor of an audio D / A converter, in order to reduce the time required for measuring the distortion factor, a pre-stage of this effective value detection circuit is used. Of the coupling capacitor (not shown in FIG. 3) provided on the input side of the audio D / A converter, and the low-pass filter included in the audio D / A converter itself is A predetermined time constant is set so as to match the signal to be measured.

[0004]

In the conventional effective value detection circuit described above, as an example, in a D / A converter test method, a small amplitude sine wave signal is added with an offset voltage that changes stepwise. However, when measuring the distortion at each step, the change in the offset voltage is directly input to the effective value detection circuit as noise, so that the detection output of the effective value detection circuit adheres to the maximum output voltage. After that, the output characteristic gradually decreases to the original measured value due to the time constant of the low-pass filter.
In addition, the distortion measurement method in the test method of the D / A converter is an extremely large measurement method in which the number of measurements rises to several hundred steps, and the distortion measurement time per step is reduced as much as possible. Is required.

However, the conventional effective value detection circuit receives the analog input signal 101 output from the corresponding audio D / A converter, performs an effective value detection in the effective value detector 31, and then outputs the resistance value. Although the effect of reducing the ripple contained in the detection output 102 is effectively obtained by the low-pass filter formed by the capacitor, no measure is taken to reduce the measurement time. For this reason, the time required for the effective value detection signal 103 to be output in a stable state is lengthened by the secondary low-pass filter, and a great amount of time is required for measuring the distortion of the audio D / A converter. There is a disadvantage that it requires.

[0006]

According to a first aspect of the present invention, there is provided an effective value detection circuit which receives a signal to be detected, detects an effective value of the signal, and outputs the signal. A low-pass filter that receives a detection output of the detector and reduces a ripple included in the detection output to output a predetermined effective-value detection signal. A diode having a cathode connected to the output terminal of the effective value detector, an anode connected to the output terminal of the effective value detection circuit, a resistor connected in parallel with the diode, and the effective value detection. It is provided with a capacitor connected between the output terminal of the circuit and the ground point.

An effective value detection circuit according to a second aspect of the present invention includes an effective value detector for inputting a signal to be detected, detecting an effective value of the signal, and outputting the signal, and a detection device for the effective value detector. And a low-pass filter configured to input an output and reduce a ripple included in the detection output to output a predetermined effective-value detection signal, wherein the low-pass filter includes: A resistor connected between the output terminal of the value detector and the output terminal of the effective value detection circuit, and a capacitor connected between the output terminal of the effective value detection circuit and a ground point, An analog switch connected in parallel to the resistor corresponding to a low-pass filter, and an analog that detects a maximum output voltage value of a detection output of the effective value detector and controls the analog switch to close. Switch control It is characterized in that it comprises a stage.

The analog switch control means includes:
A comparator that compares a detection output voltage value of the effective value detector with a predetermined threshold level value, detects a maximum output voltage value of the detection output, and outputs a predetermined determination level value; And a delay circuit that delays by a predetermined time and outputs the signal as an open / close control signal for the analog switch.

[0009]

Next, the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing a first embodiment of the present invention. As shown in FIG. 1, this embodiment uses an analog input signal 10 output from an audio D / A converter.
1, an effective value detector 11 for detecting the effective value of the analog input signal 101 and a detection output 102 of the effective value detector 11 are input and integrated to suppress a ripple included in the detection output to obtain a predetermined value. , A resistor 12 and a diode 14 and a capacitor 13 connected in parallel as components of a secondary low-pass filter for outputting an effective value detection signal 103 of
And a low-pass filter formed by the above.
The internal configuration of the effective value detector 11 is the same as that of the above-described conventional example, and the low-pass filter including the diode 14 is called a secondary low-pass filter as described above.

In FIG. 1, the present embodiment differs from the conventional example in that a diode 14 functioning as a precharge circuit is newly added as a component of the secondary low-pass filter. The basic operation of the present embodiment is the same as that of the conventional example. The analog input signal 101 output from the audio D / A converter is input to the effective value detector 11 and subjected to effective value detection. A detection output 102 is output and input to the second-order low-pass filter. In this secondary filter, the ripple included in the detection output 102 is removed and output as an effective value detection signal 103. In the secondary low-pass filter, the diode 14 is connected in parallel to the resistor 12, and this embodiment is used. During the effective detection operation, the voltage level of the effective value detection signal 103 output from the secondary low-pass filter is equal to the detection output 1 of the effective detector 11.
Becomes a V _F only higher levels of the diode 14 than the 02 voltage level, the diode 14 at the time
Becomes conductive, thereby increasing the response speed of the secondary low-pass filter and shortening the measurement time of the distortion factor.

As an example, suppose that the time constant of the effective value detector 11 and the time constant of the second-order low-pass filter are the same value, and the ripple reduction rate for the second-order harmonic distortion by the second-order low-pass filter is 1 /. Assuming that the measured voltage value is 1/10 of the maximum output voltage value of the effective value detector 11 as 100,
When a fundamental signal of 1 KHz is used, a stabilization time of 12.5 ms is required for measurement without the diode 14, whereas in this embodiment, 10.5 ms is required.
A result of stabilization in ms is obtained. That is, the measurement stabilization time is reduced by about 15%.

FIG. 2 is a block diagram showing a second embodiment of the present invention. As shown in FIG. 2, in the present embodiment, the analog input signal 1 output from the audio D / A converter
01, the effective value detector 21 for detecting the effective value of the analog input signal 101 and the detection output 102 of the effective value detector 21 are input and integrated, and the ripple included in the detection output 102 is suppressed. A predetermined effective value detection signal 103
, A secondary low-pass filter including a resistor 22 and a capacitor 23 for outputting a signal, and an analog switch 24 connected in parallel to the resistor 22 corresponding to the secondary low-pass filter.
26, a comparator 26 for comparing the detection output 102 of the effective value detector 21 and the output voltage of the DC power supply 25, a DC power supply 25 for supplying a predetermined threshold level to the comparator 26, and a comparison determination output output from the comparator 26. And a delay circuit 27 for delaying the analog switch 104 by a predetermined time and outputting the control signal 105 to the analog switch 24. The internal configuration of the effective value detector 11 is the same as that of the above-described conventional example.

In FIG. 2, a comparator 26 supplies a voltage supplied from a DC voltage source 25 to a negative-phase input terminal,
A threshold level slightly lower than the maximum output voltage of the detection output 102 output from the effective value detector 21 is set in advance. The analog input signal 101 output from the audio D / A converter is applied to an effective value detector 2
1 and is subjected to effective value detection, and the detection output 102 is input to the positive-phase input terminal of the comparator 26 and the secondary low-pass filter. Initially, the analog switch 24 included in the secondary filter is in an open state, so that the secondary low-pass filter operates by being formed by the resistor 22 and the capacitor 23 in the first stage.

The voltage level of the detection output 102 of the effective value detector 21 increases in accordance with the input level of the analog input signal 101 output from the audio D / A converter,
When approaching the maximum output voltage value, the comparator 26 enters a state where the voltage level of the detection output 102 exceeds the threshold level.
It is determined that the voltage level of the detection output 102 of the effective value detector 21 is stuck to the maximum output voltage, and the comparator 26 outputs a comparison determination output 104 of a predetermined level, which is input to the delay circuit 27. In the delay circuit 27, the comparison judgment output 104 is output after being delayed by a predetermined time (set to a time approximately 3 to 5 times the time constant of the effective value detector 21), and is input to the analog switch 24 as a control signal 105. Is done. The analog switch 24 is closed when receiving the control signal 105, the resistor 22 is short-circuited by the analog switch 24, and the time constant of the secondary low-pass filter is set to an extremely small value. . As a result, the response speed of the second-order low-pass filter becomes extremely fast, the state where the secondary low-pass filter is attached to the maximum output voltage value is avoided, and the measurement time of the distortion factor is reduced.

As an example corresponding to the operation of the present embodiment, it is assumed that the time constant of the effective value detector 21 and the time constant of the secondary low-pass filter are set to the same value, that is, 0.8 ms. When the maximum output voltage of the output is 10 V, the measured voltage value is 1 V, and the ripple is 0.1 V, the voltage level of the detection output 102 of the effective value detector 21 is 3.7 ms and the voltage level of the ripple is Stabilizes to the same level. Therefore, when the time in the delay circuit 27 is set to 3.7 ms, 0 to 99% of the required stabilization time from the point of the maximum voltage output value at the detection output 102 of the effective value detector 21 to the time when the measured voltage value is reached is reached. Until
Since the analog switch 24 is closed, the time constant of the secondary low-pass filter is such that the resistor 22
4, which is short-circuited to 0 ms, and the effect is obtained that the measurement time is shortened within the stabilization time for one stage of the secondary low-pass filter.

In the above setting conditions, 0 to 9
The stabilization time corresponding to 9% is 3.7 ms, 99-9
The stabilization time corresponding to 9.9% is 4.8 ms, and it is possible to measure the predetermined distortion rate in 8.5 ms in total.

In comparison between the present embodiment and the conventional example, under the same conditions as described above, a conventional effective value detection circuit without a precharge circuit requires a stabilization time of at least 12.5 ms. Yes, so
In this embodiment, the stabilization time is reduced by about 30% as compared with the conventional example.

[0019]

As described above, the present invention is applied to an effective value detecting circuit used for measuring a distortion factor, and a precharge circuit is added to a secondary low-pass filter included in the effective value detecting circuit. With this arrangement, the output stabilization time of the effective detection signal obtained as a measured value is 10 to 3
There is an effect that it can be reduced by 0%.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a first embodiment of the present invention.

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

FIG. 3 is a configuration diagram showing a conventional example.

[Explanation of symbols]

 11, 21, 31 RMS detector 12, 22, 32 Resistance 13, 23, 33 Capacitor 14 Diode 24 Analog switch 25 DC power supply 26 Comparator 27 Delay circuit

Continuation of the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01R 19/02 G01R 19/04 G01R 23/20

Claims (3)

(57) [Claims] An effective value detector for inputting a signal to be detected and performing an effective value detection of the signal, and a detection output of the effective value detector are input and included in the detection output. A low-pass filter configured to output a predetermined effective value detection signal by reducing ripples, wherein the low-pass filter has a cathode connected to an output terminal of the effective value detector. A diode having an anode connected to the output terminal of the effective value detection circuit, a resistor connected in parallel with the diode, and a capacitor connected between the output terminal of the effective value detection circuit and a ground point; And an effective value detection circuit characterized by comprising: 2. An effective value detector for inputting a signal to be detected and performing an effective value detection of the signal, and a detection output of the effective value detector, and including the detection output. A low-pass filter configured to output a predetermined effective-value detection signal by reducing a ripple, wherein the low-pass filter includes an output terminal of the effective-value detector and the effective-value detection. A resistor connected between the output terminal of the circuit and a capacitor connected between the output terminal of the effective value detection circuit and a ground point. An analog switch connected in parallel, and analog switch control means for detecting a maximum output voltage value of a detection output of the effective value detector and controlling the analog switch to close the analog switch. Effective Detection circuit. 3. The analog switch control means compares and compares a detected output voltage value of the effective value detector with a predetermined threshold level value to detect a maximum output voltage value of the detected output. The effective value detection circuit according to claim 2, further comprising: a comparator that outputs a value; and a delay circuit that delays the determination level value by a predetermined time and outputs the result as an open / close control signal for the analog switch.