JPH02307072A - Frequency decision circuit - Google Patents

Abstract

PURPOSE:To decide a frequency with small-sized circuit constitution by detecting a saw-tooth wave voltage, obtained by charging and discharging a capacitor by a constant-current source and a switch circuit, by an analog comparator. CONSTITUTION:When a signal applied as an object of frequency decision making to a signal input terminal 11 is inputted to the capacitor 13 through a transistor(TR) 12 constituting the switch circuit. The capacitor 13 is charged electrically by the constant-current source 14 through a resistance 15 and discharged through a resistance 15 with an input signal from the signal input terminal 11. The capacitor 13 is connected to the plus input terminal of the analog comparator 16, a variable resistor 17 is connected to the minus input terminal of the analog comparator 16 and a slice voltage is inputted. The output of the analog comparator 16 is held by a holding circuit 18 and its frequency decision result is outputted from an output terminal 9. The holding circuit 18 is concretely, for example, a one-shot circuit.

Description

DETAILED DESCRIPTION OF THE INVENTION FIELD OF INDUSTRIAL APPLICATION The present invention relates to a frequency discrimination circuit for handling several known types of frequencies.

Conventional technology FIG. 3 shows the configuration of a conventional frequency discrimination circuit.

In FIG. 3, a signal applied to signal input terminal 1 whose frequency is to be determined is input to counter circuit 2, and a reference signal for periodically clearing counter circuit 2 is input from reference period signal input terminal 3. Ru. The output signal of the counter circuit 2 is input to the digital comparator circuit 4, roughly the set value signal is input from the comparison value setting terminal 5 to the digital comparator circuit 4, and the comparison result of the digital comparator 4 is held in the holding circuit 6. The frequency discrimination result is output from the output terminal 7.

In the above configuration, an operation for determining two types of frequencies, high and low, will be described. The counter circuit 2 periodically counts up the input signal applied to the signal input terminal 1 from 1 based on the reference signal applied to the reference period signal input terminal 3, as shown in FIG.

First, when a high frequency input signal is applied, the output of the counter circuit 2 exceeds the set value of the comparison value setting terminal 5 within one period of the reference signal, as shown in FIG. The comparator circuit 4 outputs “Hn” to the holding circuit 6.
(or 'L') level signal.The holding circuit 6 holds the output for one period or more of the reference signal, and outputs an H' (or 'L') level DC voltage to the output terminal 7.

Next, when a low frequency input signal is applied, the output of the counter circuit 2 does not exceed the set value of the comparison value setting terminal 5, as shown in FIG. The holding circuit 6 continues to output an “L” (or H”) level signal to the output terminal 7, and the holding circuit 6 also outputs an “L” (or H”) level signal to the output terminal 7.
or "H") level DC voltage is output.

Problem to be Solved by the Invention The conventional circuit described above has a large circuit scale and also requires a circuit for changing the reference signal. In addition, when dealing with differences between relatively low frequencies, it takes a long time to perform the discrimination, which is inappropriate.

The present invention solves this problem, and aims to provide a frequency discrimination circuit that can be configured relatively easily.

Means for Solving the Problems In order to solve the above problems, the frequency discrimination circuit of the present invention includes a constant current source, a capacitor charged by the current, and an analog comparator to which the lamp voltage generated by the capacitor is input. and switch means for discharging the charging voltage of the capacitor according to a periodically input signal, the input signal discharging the capacitor periodically depending on whether the ramp voltage exceeds the slice voltage of the analog comparator. It is designed to determine the frequency of

Effect With the above configuration, the analog comparator detects the sawtooth waveform voltage obtained by charging and discharging the capacitor using the constant current source and the switch means, and the high or low frequency of the input signal can be determined from the output. This eliminates the need for a counter circuit and allows frequency discrimination to be made within one cycle of the input signal.

Example An embodiment of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram of a frequency discrimination circuit showing one embodiment of the present invention. In FIG. 1, the voltage ξ applied to the signal input terminal 11
A signal whose frequency is to be determined is input to a capacitor 13 via a transistor 12 forming a switch circuit. The capacitor 13 is charged by the constant current source 14 through the resistor i15, and discharged through the switch circuit 112 by the input signal from the signal input terminal 11. The capacitor 13 is connected to the Φλ input terminal of the analog comparator 16, and the variable resistor 1 is connected to the O input terminal of the analog comparator 16.
7 is connected to input the slice voltage. The output of the analog comparator 16 is held in a holding circuit 18, and the frequency discrimination result is outputted from an output terminal 19. Specifically, the holding circuit 18 is, for example, a one-limit circuit.

In the above configuration, an operation for determining two types of frequencies, high and low, will be described. First, when an input signal with a low frequency &1 number is applied to the input terminal 11, while the input signal is at L'' level, the capacitor 13 is charged by the constant voltage R source 14 via the resistor Fc15, so the Φλ input of the analog comparator 16 A ramp voltage V1 shown in FIG.
At this time, the output Vo of No. 6 outputs the uHn level.

The holding circuit 18 receives this signal and outputs “H” to the output terminal 19.
"(or "L") level DC voltage is output.

After that, when the input signal becomes "H", the transistor 12 is turned on, the charge in the capacitor 13 is discharged, and the output V+ of the analog comparator 16 becomes "L" level.

Next, when a high frequency input signal is applied to the input terminal 11, the ramp voltage V+ shown in FIG. 2(b) is generated at the Φλ input terminal of the analog comparator 16 while the input signal is at the "L" level, as described above. Since the input signal reaches the "H" level before exceeding the slice voltage V- and discharges the capacitor 13, the output terminal 19 remains at the "L" (or 'H') level.

Effects of the Invention As described above, by using the frequency discrimination circuit according to the present invention, frequencies can be easily discriminated with a small-scale circuit configuration.

[Brief explanation of drawings]

FIG. 1 is a circuit diagram of a frequency discrimination circuit according to an embodiment of the present invention;
FIG. 2 (aHb) is an explanatory diagram of the operation of the same frequency discriminating circuit, FIG. 3 is a circuit diagram of a conventional frequency discriminating circuit, and FIG. 4 is an explanatory diagram of the operation of the conventional example. 11... Signal input terminal, 12... Transistor for forming a switch circuit, 13... Capacitor, 14...
Constant current source, 15... Resistor, 16... Analog comparator, 17... Variable resistor, 18... Holding circuit,
19...Output terminal, Vl...Lamp voltage, ■--
・Slice voltage. Agent Yoshihiro Morimoto Figure 1 and Power Translation □

Claims (1)

[Claims] 1. A constant current source, a capacitor charged by the current, an analog comparator to which the lamp voltage generated by the capacitor is input, and a switch that discharges the charging voltage of the capacitor by a periodically input signal. and a frequency determining circuit configured to determine the frequency of an input signal that periodically discharges the capacitor depending on whether the ramp voltage exceeds the slice voltage of the analog comparator.