JPS604432B2 - frequency signal voltage signal converter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a frequency signal to voltage signal converter that converts a frequency signal into a voltage signal of a corresponding magnitude.

Conventionally, as this type of device, a combination circuit of a monostable multipipulator and a smoothing circuit that converts an input frequency signal into a pulse signal with a constant pulse width has been generally used.

However, such conventional devices have the disadvantage that the circuit configuration is complicated and that conversion errors occur because the pulse width, which should be constant, is affected by temperature. The present invention eliminates the drawbacks of such conventional devices, and
The aim is to realize this type of converter with low power consumption.

FIG. 1 is a block diagram showing the basic circuit of the present invention.

In the figure, 1 is an input terminal to which a frequency signal to be converted is applied; 2 is a time constant circuit composed of a resistor R and a capacitor C; C. - The time constant determined by R should be selected to be sufficiently smaller than the pulse width of the input frequency signal. 3 is Exlusive O
R) circuit (hereinafter referred to as an ExOR circuit), an input frequency signal is applied to one input terminal, and an output signal of the time constant circuit 2 is applied to the other input terminal.

4 is a smoothing circuit which receives the output signal of the ExOR circuit and obtains a voltage signal corresponding to the input frequency signal, and 5 is an output terminal.

The operation of the circuit constructed in this manner will now be described with reference to FIG.

Now, if a pulse signal of height Vs and pulse width t as shown in Fig. 2A is applied to input terminal 1, ExOR
This is applied as is to one input terminal of the circuit 3, and the C. - A delayed pulse signal is applied that rises with a time constant of R and falls with the same time constant. The ExOR circuit 3 determines whether the states of the signals applied to the two input terminals are 1'', 0'' or 0.
When ``, i1'', 1'' is output, and when 1'', i1'' or 0'', 0'', o'' is output. If the threshold voltage for determining 1'' and 0 is set to ET in Figure 2, the output signal will be two pulse signals as shown in Figure 2C. That is, a pulse signal is output during the time period from when the output of the time constant circuit 2 reaches ET from zero, and from Vs to ET, and the frequency of this pulse signal is twice the input frequency. . The smoothing circuit 4 receives the output pulse of the ExOR circuit 3 shown in FIG. 2C, and obtains a DC voltage corresponding to the input frequency as shown in FIG. 2B. Here, the influence of temperature changes on the circuit shown in FIG. 1 will be considered.

In this circuit, if the circuit constants of the time constant circuit 2 and the smoothing circuit 4 are ignored with respect to temperature changes, temperature changes mainly cause changes in the threshold voltage ET of the ExOR circuit 3. . Now, if the threshold voltage near room temperature is E', and the voltage indicating the height of the pulse signal applied to the input terminal is Vs, then
These and the time widths t,,t of the two pulse signals obtained
2 can be shown by the {1} formula and the [2} formula, respectively. -tl VSku・-e C. R, )=ET (1) t2
■Vs e C,R,=ET However, C,,R, is the time constant of time constant circuit 2 From equation '1) and equation {2}, the time width of the pulse signal, t2 is the glue equation and '4, respectively. }It can be shown by the formula.

*t・=−CIR
・log(1-su)'3't2=-c,R,10
[4' The DC voltage Vo obtained through the smoothing circuit 4 is
The sum of the areas of the two pulse signals obtained in circuit 3 (corresponds to the sum of the shaded areas in Figure 2'), that is, if the pulse height is constant, corresponds to the sum of time widths t and t2. do.

Therefore, the DC voltage Vo obtained through the smoothing circuit 4
is represented by the formula {5). V. =t, tent2=-C. R
．． logET.

ET) '5} Here, if the temperature changes by △T from room temperature and the threshold voltage of the ExOR circuit decreases by △ET and becomes ET - △ET, then the two pulse signals obtained are The pulse width et al., t2, is '6
} expression, {7] expression. t,. =-C. R. log
(・-E three hands three) [61t2. =-C. R.・0g
ET-Vsha ET '71 Furthermore, the DC voltage Vo obtained through the smoothing circuit 4 is represented by the formula '8}.
V.

,=t,. 10t2,=-C,R,-.

gET-△ET) Ws-ET+△ET) Vs2=・C,
R.J.

gETWs-ET)+(but,-Vs)△E,-(△E,
In equations (5) and (8), ET=1'
Assuming 2Vs, these equations are expressed as a glue equation and a dish equation, respectively.

V.

=tl+t2:-CIRI10g amount ■V〇,=t
、． 10t2, :-C・R・log{Kiichibe)2} In seed 10, ET2/Vs2 becomes a sufficiently small value, so if this is ignored, 10 becomes the same as the formula [9}.

That is, the DC voltage obtained via the smoothing circuit 4 is hardly affected by temperature changes. FIG. 3 is a waveform diagram conceptually explaining the above operation. In Figure 3A, when the threshold voltage ET decreases by △ET, the time width of the first pulse signal, as shown in Figure 3C, becomes smaller than the time width L' shown in Figure 3A. becomes smaller,
The time width t2 of the second pulse signal is larger than the time width t2 shown at the beginning of FIG. Therefore, the sum of the time widths of the first pulse signal and the second pulse signal t...+
are maintained at approximately the same value as t and t2. Even when the threshold voltage increases by △ET, the time width t,2 of the first pulse signal increases, and the time width t,2 of the second pulse signal increases, as shown in FIG. Although it becomes smaller, the sum of the time widths of both pulse signals, t, 20, 22, is maintained at approximately the same value as t, 10, t2. Note that the BxOR circuit composed of C-MOS has the characteristic that its threshold voltage is 1'2 of the applied signal voltage at around room temperature.
If this is used in the circuit according to the present invention, the effects of the present invention can be easily achieved.

FIGS. 4 and 5 are block diagrams showing other embodiments of the present invention.

In each of the embodiments, a circuit is added to each input terminal of the ExOR circuit 3 for adjusting the height (amplitude) of the pulse signal applied to the input terminal of the ExOR circuit 3 to a constant value. That is, in the embodiment shown in FIG. 4, AND gate circuits 61 and 71 each having one input terminal supplied with a constant voltage Vs are added to the input terminal of the ExOR circuit 3. Further, the embodiment shown in FIG. 5 includes OR circuits 81 and 91 whose one input end is connected to a common line. As explained above, according to the present invention, the main circuit elements are a time constant circuit composed of a resistor and a capacitor, an ExOR circuit, and a smoothing circuit, and the overall circuit configuration is simple and consumes little power. Moreover, it is possible to realize a frequency signal/voltage signal converter that is almost unaffected by temperature.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the basic circuit of the present invention, Figure 2 is a waveform diagram to explain the operation of the circuit in Figure 1, and Figure 3 is a waveform diagram to explain the influence of temperature changes on the circuit in Figure 1. The waveform diagram, FIGS. 4 and 5 are block diagrams showing other embodiments of the present invention. 1...Input terminal, 2...Time constant circuit,
3... Exclusive OR circuit, 4... Smoothing circuit, 5... Output terminal. Younger brother' figure 2 younger brother 3 figure younger brother 4 figure multiple J figure

Claims (1)

[Claims] 1. A time constant circuit that is composed of a resistor and a capacitor and receives the frequency signal to be converted as an input, and has the frequency signal to be converted as one input and the output signal of the time constant circuit as the other input, and an input signal that is given. a logic circuit including an exclude-or circuit made of C-MOS in which a threshold voltage exists near approximately 1/2 of the voltage;
A frequency signal voltage signal converter comprising a smoothing circuit that smooths the output signal of the logic circuit and obtains a voltage signal corresponding to the frequency signal.