JPH04140923A - Identification circuit converting analog signal into digital signal - Google Patents

Abstract

PURPOSE:To reduce the cost by employing an inexpensive general-purpose gate IC and to prevent the effect of a temperature change by using a DC voltage generating circuit to apply temperature compensation of an input threshold voltage to the general-purpose IC. CONSTITUTION:A voltage adder circuit 11 employs an operational amplifier OP1 and a DC voltage generating circuit 12 employs a diode D1 for temperature compensation of an input threshold voltage Vth of a general-purpose gate IC 13 and an AND gate IC1 is used for the IC 13. An analog signal inputted to an input terminal 10 is added to a DC output voltage Ve of the circuit 12 by the circuit 11 comprising resistors R1, R2, R3 and R4 and the OP1. The DC output voltage Ve is obtained by dividing an applied voltage Va to the circuit 12 by a variable resistor VR1. The voltage Ve is adjusted by the resistor VR1 so as to identify a low level and a high level at the input threshold voltage Vth to the IC1. The output of the circuit 11 is converted into a digital signal by the IC1 and outputted to an output terminal 14.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an identification circuit used in a demodulator of a digital transmission system.

[Prior Art] In a digital transmission system, an identification circuit that identifies whether an input analog signal is a low level or a high level, converts it into a binary digital signal, and outputs it has a fifth
A comparator (voltage comparator) as shown in the figure is generally used. This comparator compares the level of the input signal with a reference voltage Vr@t, which is a threshold voltage, to obtain a reference voltage V,. , outputs a high level when the input signal level is large and outputs a low level when it is small.

For example, an analog signal of amplitude vd, as shown in Figure 6A, sets the comparator threshold voltage to Vd.
When set to d/2, it is converted into a digital signal as shown in No. 6B.

In this case, the reference voltage V,. If f is stable with respect to temperature changes, the threshold level of the comparator is also always constant, so the identification circuit is not affected by temperature changes.

1゛Problems to be Solved by the Invention] By the way, when using a comparator (or in a conventional identification circuit), as the data transmission speed increases, a general-purpose comparator cannot keep up with the rising speed of the signal.・If the transmission speed is fast, it becomes necessary to use an expensive ultra-high-speed comparator made of ECL (emitter coupled logic), etc., and the cost of the identification circuit becomes extremely high. There was a problem.

In view of the problems of the prior art, the present invention aims to provide an identification circuit that is inexpensive and unaffected by temperature changes without using an expensive ultra-high-speed comparator.
I have a purpose.

According to the present invention, the identification circuit that converts an analog signal into a digital A voltage adder circuit for converting the output of the voltage adder circuit into a digital signal (1-IC
As a feature, the L/bevel variation of the output voltage of the DC voltage generation circuit in response to temperature change is substantially the same as the level variation of the input cuff and threshold voltage of the general-purpose gate 11c, ing.

1 Effect] The identification circuit according to the present invention uses an inexpensive general-purpose gate IC, so the cost is low, and the DC voltage generation circuit (J) performs temperature compensation of the input threshold voltage of the general-purpose game HLC. Therefore, it is not affected by temperature changes.

[Embodiment] FIG. 1 shows a block diagram 1 of an identification circuit according to an embodiment of the present invention. This identification circuit is the voltage adder circuit 2. DC current l]-Cow generating circuit 12. General purpose gate I
It is equipped with C1 and C3. Identification circuit 10 input terminal r1.0
/l:, '7 The analog signal is input to the DC voltage generating circuit 1. in the electric f1/addition circuit 11-. The output type j-T, J-is added 7, and the output of the voltage adder circuit 11 is a general-purpose game. In addition,
Goko +75-・) The general-purpose gate ICl3 includes an AND game h, an OR gate, a NOT gate (inverter), etc.
Commonly used basic gate ICs are included 9,
These general-purpose gates 5 and 1-ICl3 control the low level and high level of the signal 5 and 1, respectively, depending on the internal input threshold voltage Vrh.
Identifies the bell. That is, if the output signal of the voltage adder circuit 11 is higher than .about.h, a high level is output to the output terminal 14 of the general-purpose game hIc13, and if it is lower than V't1, a low level is output. Just [5, for example NOT
Depending on the type of gate used, an inverted output may appear at the output terminal 14, such as when a gate (inverter) is used.

Incidentally, the input threshold voltage Vch of the general-purpose gate ICl3 generally has temperature dependence7, and V+h changes as shown in FIG. 3 with respect to temperature changes.

Therefore, if the temperature changes, the pulse width of the output signal will also change due to the drift of V'+h2, and correct data will not be transmitted.

Therefore, in the present invention, the inexpensive general-purpose gate ICl3 can be used for temperature change control. In order to use the identification circuit ``ζ'' which is not affected by
~) Temperature compensation for I C1, 3 is performed. In other words, the temperature dependence of the output voltage of the DC voltage generation circuit is shown in Figure 3. This is substantially the same as the temperature dependence of Vth.

FIG. 2 is a circuit diagram showing an example of the contents of the block diagram of the identification circuit shown in FIG. 'J. In this specific example, the voltage adder circuit 11 is configured using an operational amplifier OP1. The DC voltage generation circuits 1 and 2 are general-purpose voltage generators
x3 input threshold voltage V, ; , diodes for temperature compensation). AND gate ICI is used for general-purpose gates IC1 and IC3. In such an identification circuit, the analog signal input to the input terminal ]-0 is input to the voltage adder circuit 1, 1 composed of resistors R3゜R, 2, R3, and R4 and an op/op OP'l. , are added to the self-current output voltage ve of the DC voltage generation circuit 12. DC output voltage■. is obtained by dividing the voltage Va applied to the DC voltage generation circuit 12 using a variable resistor VRI. V.

The value of is adjusted by the variable resistor VRI so that low level and high level can be discriminated by the input threshold voltages V and h of the AND gate ICI in the subsequent stage. The output of the adder circuit 11 is converted into a digital signal by an AND gate ICI and output to an output terminal 14.

In addition, in the identification circuit of FIG. 2, the AND gate IC
The temperature characteristics of the diode D1 are utilized as a countermeasure against the drift of the threshold voltage v+h of I due to temperature changes. That is, this problem is solved by causing the output voltage V8 of the DC voltage generation circuit 12 to drift in the same manner as Vth depending on the temperature characteristics of the diode D1.

More specifically, the If-Vf characteristic, which represents the relationship between the forward current 1 of the diode D1 and the forward voltage Vf, is as shown in FIG. It has a temperature characteristic such that the higher V becomes, the smaller V becomes. Therefore, by adjusting the bias current 1° flowing through the diode D1, the temperature change can be reduced.

The drift of △Vl is the drift of Vth △V.

It can be equal to 5.

As a result, it is possible to construct a stable identification circuit in which the pulse width of the output signal is not affected by temperature changes.

[Effects of the Invention] As described above, according to the present invention, an inexpensive identification circuit can be provided by using a general-purpose gate IC,
Moreover, since the input threshold voltage of the general-purpose gate IC is temperature-compensated by the DC voltage generation circuit, it is possible to provide an identification circuit that is not affected by temperature changes.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an identification circuit according to one embodiment of the present invention. FIG. 2 is a circuit diagram showing a specific example of the identification circuit shown in FIG. 1. FIG. 3 is a graph showing the temperature dependence of the input threshold voltage in a general-purpose gate IC. FIG. 4 is a graph showing the temperature dependence of the ItVr characteristic of the diode. FIG. 5 is a block diagram showing a conventional identification circuit. FIG. 6A is a diagram showing input signals of the identification circuit. FIG. 6B is a diagram showing the output signal of the identification circuit. In the figure, 1 is an identification circuit, 10 is an input terminal, 11 is a voltage addition circuit, 12 is a DC voltage generation circuit, 13 is a general-purpose gate IC, and 14 is an output terminal. Note that in each figure, the same reference numerals indicate the same contents or corresponding parts. Figure 1 Figure 2 Figure 3 Purpose-111--~ Concentration Figure 4 Figure 5 Figure 6A Figure 6B

Claims (1)

[Scope of Claims] An identification circuit for converting an analog signal into a digital signal, comprising: a DC voltage generation circuit; a voltage addition circuit for adding an output voltage of the DC voltage generation circuit to the analog signal; and the voltage and a general-purpose gate IC for converting the output of the adder circuit into the digital signal and outputting the digital signal, and the level fluctuation of the output voltage of the DC voltage generation circuit due to temperature change is equal to the level fluctuation of the input threshold voltage of the general-purpose gate IC. An identification circuit characterized in that it is substantially identical to a minute.