JP2576414B2 - AC level 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 AC signal level detection circuit, and more particularly to a temperature stable detection circuit.

[0002]

2. Description of the Related Art In a conventional temperature compensation type level detection circuit,
As shown in FIG. 2, when the level of the AC signal 1 is detected by the detection diode 2, when a small AC voltage is detected, a bias is applied to the voltage source 8 and the resistor 4 until a slight current flows in the forward direction of the diode 2. And the second diode 3 is biased by the resistor 5, and the diodes 2 and 3
Have the same characteristics, the resistors 4 and 5 have the same value, and the differential amplifier 9
Therefore, by amplifying and outputting the difference between the terminal voltages of the two diodes, the fluctuation of the terminal voltage of the diode 2 due to the temperature change is canceled. In the circuit of FIG.
The level of the AC signal 1 is detected by utilizing the fact that the terminal voltage of the diode 2 changes according to the magnitude of the AC signal 1 and that the output of the differential amplifier 9 fluctuates according to the magnitude of the AC signal 1. I have.

The variation of the bias point of the diode 2 due to temperature can be avoided by employing the circuit shown in FIG. 2. However, as shown in FIG. 3, in the diode, the differential value of the voltage-current characteristic changes with temperature, and Even with current, the detection output decreases as the temperature decreases.

Therefore, conventionally, as shown in FIG. 2, a voltage dividing circuit having a larger voltage dividing ratio as the temperature rises by the resistor 10 and the thermistor 11 is provided, and the result of compensating the fluctuation of the detection efficiency is output to the output terminal. I had 12

[0005]

In this conventional system,
There are two temperature-compensating elements, that is, temperature-sensitive elements, the diode 3 and the thermistor 11, and it is necessary to thermally couple both of them to the detection diode 2 for mounting, which complicates the structure. . Also, it is originally troublesome to adjust a diode and a thermistor having different temperature characteristics so that the characteristics cancel each other.

[0006]

In order to solve the above-mentioned problems, the present invention provides the following means.

A circuit for detecting the magnitude of the AC signal by detecting the AC signal with a first semiconductor diode, wherein a current bias is applied to apply an optimum bias to the first semiconductor diode, and The same amount of bias current is applied to the second semiconductor diode having the same characteristics as the first semiconductor diode, and the DC current flowing through both semiconductor diodes or the terminal voltage of both semiconductor diodes is applied to the differential amplifier. Utilizing that the output changes according to the magnitude of the AC signal applied to the first semiconductor diode, the level of the AC signal is detected by the output of the differential amplifier, and the level of the first semiconductor diode is detected. In a level detection circuit configured to compensate for a temperature change of a bias point, the level detection circuit may be configured to respond to a terminal voltage of the second semiconductor diode. AC level detector circuit for controlling the gain of the level signal amplification system comprising the differential amplifier.

[0008] A first resistor is connected in series to the first semiconductor diode, and a second resistor is connected to the second semiconductor diode.
Are connected in series, a first DC circuit comprising the first semiconductor diode and the first resistor, and a second
A second DC circuit composed of a semiconductor diode and a second resistor is connected in parallel, a DC voltage for the current bias is applied, and a first point, which is a connection point between the first semiconductor diode and the first resistor, is connected. The AC level detection circuit as described above, wherein a node and a second node, which is a connection point between the second semiconductor diode and the second resistor, are respectively connected to a differential input terminal of the differential amplifier. .

The level signal amplifying system includes the differential amplifier and a variable gain amplifier for amplifying the output of the differential amplifier. The gain of the variable gain amplifier depends on the terminal voltage of the second semiconductor diode. The AC level detection circuit according to the above or the above, wherein

The AC level detection circuit as described above, wherein the terminal voltage of the second semiconductor diode is amplified by a second differential amplifier and applied to a gain control terminal of the variable gain amplifier.

[0011]

In the present invention, since the gain of the level signal amplification system is controlled by the terminal voltage of the second diode, even if the detection efficiency of the diode fluctuates with temperature, the fluctuation can be compensated for in the level signal amplification system. .

[0012]

FIG. 1 is a circuit diagram of an embodiment of the present invention.

The terminal voltage of the compensation diode 3 is amplified by the differential amplifier 21 to control the gain of the variable gain amplifier 22. The variable gain amplifier 22 amplifies and outputs the output of the differential amplifier 9 for amplifying the difference between the terminal voltages of the two diodes 2 and 3.

For example, as the temperature becomes lower, the diodes 2 and 3
, And the output obtained by inverting and amplifying the voltage by the differential amplifier 21 becomes a voltage proportional to the temperature, whereby the gain of the variable gain amplifier 22 is controlled to increase. If the relationship between the control voltage and the gain is appropriately selected in advance with respect to the temperature change of the differential value of the current and voltage of the detection diode, the change in the detection efficiency due to the temperature can be canceled.

[0015]

As described above, the present invention compensates for the change in the detection efficiency by the change in the terminal voltage of the bias current compensating diode due to the temperature, so that another compensating element is not required and the temperature is reduced. Since the number of sensitive elements can be limited to two, that is, the detection diode and the compensation diode, there is an advantage that the structure is simple and the compensation adjustment is easy.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of one embodiment of the present invention.

FIG. 2 is a circuit diagram of a conventional example.

FIG. 3 is a diagram showing static voltage / current characteristics of a diode for explaining a temperature compensation operation.

[Explanation of symbols]

 2 Detection diode 3 Compensation diode 9, 21 Differential amplifier 22 Variable gain amplifier

Claims (4)

(57) [Claims] 1. A circuit for detecting the magnitude of an AC signal by detecting an AC signal with a first semiconductor diode, wherein a current bias is applied to apply an optimum bias to the first semiconductor diode. And the first
The same amount of bias current is applied to a second semiconductor diode having the same characteristics as the semiconductor diode of the above, and a DC current flowing through both semiconductor diodes or a terminal voltage of both semiconductor diodes is applied to a differential amplifier. First
Utilizing the fact that it changes according to the magnitude of the AC signal applied to the semiconductor diode, the level of the AC signal is detected by the output of the differential amplifier, and the temperature change of the bias point of the first semiconductor diode is detected. An AC level detection circuit for controlling a gain of a level signal amplification system including the differential amplifier according to a terminal voltage of the second semiconductor diode. 2. The first semiconductor diode has a first resistor connected in series, the second semiconductor diode has a second resistor connected in series, and the first semiconductor diode and the first resistor are connected in series. And a second DC circuit consisting of the second semiconductor diode and the second resistor are connected in parallel to apply the DC voltage for current bias, and the first semiconductor diode and the second A first node which is a connection point of the first resistor and a second node which is a connection point of the second semiconductor diode and the second resistor are connected to a differential input terminal of the differential amplifier, respectively. The AC level detection circuit according to claim 1, wherein: 3. The level signal amplifying system includes the differential amplifier and a variable gain amplifier for amplifying an output of the differential amplifier, and the variable gain amplifier according to a terminal voltage of the second semiconductor diode. The AC level detection circuit according to claim 1, wherein the gain of the AC level is controlled. 4. The AC level detecting circuit according to claim 3, wherein a terminal voltage of said second semiconductor diode is amplified by a second differential amplifier and applied to a gain control terminal of said variable gain amplifier. .