JPS5833595B2 - signal generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal generator that generates a signal proportional to a hyperbolic function of time or a logarithm of a hyperbolic function of time, which is constructed of a capacitor and a semiconductor device.

Conventionally, circuits that use capacitors and resistors to generate signals that change linearly or logarithmically over time have been widely put into practical use, but the accuracy of generating signals that are proportional to the hyperbola of time or the logarithm of the hyperbola is There was no suitable circuit with a high value.

The present invention makes it possible to obtain a hyperbolic function signal or a signal proportional to the logarithm of a hyperbolic function by skillfully utilizing the characteristics of a semiconductor device having a capacitor and a junction. Shown below.

In FIG. 1, 1 is a capacitor, and 2 is a semiconductor device connected to the capacitor 1. Here, a diode-connected transistor is shown as an example.

The semiconductor device may be a diode with a PN junction.

In this circuit, the capacitor 1 and the semiconductor device 2 are
The capacitor 1 is connected so that the potential difference e of the capacitor 1 is equal to the potential difference of the semiconductor device 2, and so that a current proportional to the current flowing through the capacitor 1 flows through the semiconductor device.

Now, a DC voltage Es is applied to the capacitor 1 via the switch S.
When S is opened after applying , the current i flowing through the capacitor 1 (here the same as the current flowing through the semiconductor device 2) and the voltage e applied to the semiconductor device 2 (here the same as the potential difference of the capacitor 1) are respectively It is expressed by equations (1) and (2).

However, C: Capacitance of capacitor 1: Boltzmann constant T Junction surface temperature of two-handed conductor device q: Electronic charge Ico: Reverse current of semiconductor device Eliminating e from equations (1) and (2) gives (3 ) formula is obtained.

In equation (3), i (o) If io, this singularity The solution is as shown in equation (4).

In equation (4), since kTC/q and kTC/qio are both constant values, the current i flowing through the capacitor 1 becomes a hyperbolic function with respect to time t, as shown in FIG.

In addition, the voltage e applied to the semiconductor device 2 can be calculated by converting equation (4) into (2
), it becomes clear that the signal is proportional to the logarithm of the hyperbolic function.

FIG. 3 is a connection diagram when the signal generator shown in FIG. 1 is applied to a circuit that converts a frequency signal into a voltage signal.

In the figure, 30 is a terminal to which a pulse train signal sf of frequency f to be converted is applied, as shown in FIG. 4A, for example;
Ml is a monostable multi-by-break triggered by this pulse train signal sf, and generates a sampling pulse PS1 as shown in FIG.

M2 is a monostable multi-by-break triggered by PSl, which generates a drive pulse PS2 of frequency f that drives the switch S as shown in FIG. 4C.

When the switch S is driven to open by Δt (Δt is determined by the circuit constant of the monostable multi-bibreak M2) by the driving pulse PS2, the capacitor 1 is charged during this time, and the semiconductor device 2 has a voltage as shown in FIG. A current flows as shown.

When the switch S is turned off, the current flowing through the capacitor 1, that is, the current i flowing through the semiconductor device 2 becomes a hyperbolic function signal as shown in equation (4) (see the waveform in FIG. 4-2).

This signal is applied to the input end of an operational amplifier OP having a feedback resistor Rf, and a signal ey as shown in equation (5) can be obtained from its output end after a time of To-Δ.

However, Rf: the resistance value of the feedback resistor Rf To: the period of the pulse signal to be converted In equation (5), if the time during which the switch S is turned on △t and/or io is set in a relationship such that △ is −kTC, then lO is obtained. Equation (5) becomes as shown in Equation (6).

As is clear from equation (6), the output signal ey of the operational amplifier OP has a value proportional to the frequency t to be converted.

The sample-and-hold circuit SH1 samples this signal ey with a sampling pulse PS1 synchronized with the next input pulse, and outputs to the output terminal 31 the dashed line in FIG. e.

Outputs a voltage signal as shown in .

Further, the sample and hold circuit SH2 samples the potential difference of the capacitor 1 and outputs a signal proportional to the logarithm of the frequency f to the output terminal 32.

Conventionally, as a circuit for converting a frequency signal into a voltage signal, there is a circuit that samples and holds the amplitude of a triangular wave signal obtained by constant current charging and short-circuit discharging of a capacitor, as described in Japanese Patent Publication No. 51-14393. but,
In such a circuit, a reciprocal conversion operation must be performed in order to obtain a signal proportional to frequency.

According to the circuit shown in FIG. 3 using the signal generation circuit according to the present invention, a signal proportional to the frequency or a signal proportional to the logarithm of the frequency can be immediately obtained without performing reciprocal conversion operations.

Now, in the device shown in FIG. 3, an error occurs due to the offset voltage of the operational amplifier OP.

In other words, if we rewrite the main part of the device in Figure 3 as shown in Figure 5 and consider this (however, the polarity of the input circuit is reversed to make the output voltage ey positive), we can see that the switch S When the capacitor 1 is turned on and the capacitor 1 is charged to a predetermined value, the following relationship is established.

Therefore, the moment the switch is turned off, the semiconductor device 2
The current i flowing through is because the initial condition is determined here.

That is, the initial value of the discharge current is i. In addition, since eoff varies depending on environmental conditions, i will vary even if io is constant, resulting in an error in the frequency conversion result.

A circuit that solves this problem is shown in FIG.

In FIG. 6, a constant current source CC is connected to the summing junction of the operational amplifier OP through a switch S,
A feedback resistor Rf, and a T-shaped circuit consisting of a capacitor 1, a semiconductor device 2, and a second feedback resistor R'f are connected between the output terminal of the operational amplifier OP and the summing junction through switches S' and S', respectively. .

The switches S', S〃 are turned on and off in conjunction with the switch S.

Switches S and S'' operate in phase, and switch S' operates in opposite phase.

When switches S and S// are on and switch S' is off, capacitor 1 is charged by current io from constant current source CC, and when switches S and S'' are off and switch S' is on, the charge on capacitor 1 is is discharged through the semiconductor device 2.

The circuit configuration during discharging becomes equivalent to the circuit shown in FIG. 5, and the output voltage ey of the operational amplifier OP becomes a hyperbolic function of time.

When the switches S and S'' are turned on and the capacitor 1 is charged to a predetermined value, the following relationship holds true.

On the other hand, the voltage applied to the semiconductor device 2 at the moment the switches S 1 and S// are turned off and the switch S' is turned on is .

That is, a voltage e1 is applied to the semiconductor device 2 in the forward direction between the collector and the emitter.

Therefore, at this time, a current i according to equation (11) flows through the semiconductor device 2, and the initial value of the discharge current is i regardless of the offset voltage of the operational amplifier OP.

Therefore, no error occurs.

As described above, according to the present invention, it is possible to realize a device that can obtain a hyperbolic function signal or a signal proportional to the logarithm of a hyperbolic function with high accuracy using an extremely simple circuit configuration.

[Brief explanation of drawings]

Fig. 1 is a connection diagram showing the principle device of the present invention, Fig. 2 is an explanatory diagram of the operation of the device shown in Fig. 1, and Fig. 3 is a connection diagram of a frequency signal voltage signal converter as an application of the device shown in Fig. 1. , FIG. 4 is an explanatory diagram of the operation of the circuit of FIG. 3, FIG. 5 is an explanatory diagram of the main part of the device of the circuit of FIG. 3, and FIG. 6 is a connection diagram showing an embodiment of the device of the present invention. 1... Capacitor, 2... Semiconductor device, S... Switch means, OP... Operational amplifier, SHl, Sn2... Sample hold. Means, M12M2... Monostable multi-bi break, CC... Constant current source, Rf. “f...Return resistance.

Claims (1)

[Claims] 1 an operational amplifier, a constant current source, a first switch that supplies the current of the constant current source to the summing junction of the operational amplifier, a first feedback resistor provided between the output terminal of the operational amplifier and the summing junction, A second switch that turns on and off in an opposite phase to the first switch and connects and disconnects the feedback path by the first feedback resistor, and a semiconductor device having a PN junction as a series limb led to the summing junction of the operational amplifier. A T-type circuit having a second feedback resistor as a series limb led to the output terminal of the operational amplifier and a capacitor as a parallel limb; A signal generation circuit comprising a third switch that connects and disconnects the series leg in which the feedback resistor is present.