JPS5853414B2 - signal detection circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a signal detection circuit for detecting a no-signal state in a tape reproducing device or the like.

1 and 2 show an example of a conventional signal detection circuit for detecting a signal state. In FIG. 1, 1 is a signal source from a magnetic tape or the like, and 2 is an amplifier.

Normally, a signal from a signal source 1 is passed through an input coupling capacitor 11, an amplifier 2, and an output coupling capacitor 12 to a rectifier circuit 3.
added to.

That is, the rectified voltage level of the rectifier circuit 3 is high when there is a signal (hereinafter referred to as a signal state), and is low when there is no signal.

This rectified voltage is applied to a Schmitt circuit 4, and an output corresponding to the presence or absence of a signal is obtained from a terminal 5.

FIG. 2 shows a specific example of the rectifier circuit 3 and the Schmitt circuit 4. In FIG.

In FIG. 2, a rectifier diode 13, a rectifier capacitor 14, and a resistor 15 form a rectifier circuit, and transistors 16 and 20
and resistors 17, 18, 19, and 21 constitute a Schmitt circuit.

Here, the attack time of the rectifier circuit is the rectifier diode 13
The recovery time is determined by the dynamic resistance of the rectifier capacitor 14 and the rectifier capacitor 14, and the recovery time is determined by the rectifier capacitor 14 and the resistor 15.

Further, the Schmitt level is determined by the ratio of resistors 17, 18 and 19 and the base-emitter voltage of transistor 16, 20.

When detecting a no-signal state on a magnetic tape, the time and signal level of the no-signal state are important.

The conventional circuit shown in FIG. 2 corresponds to recovery time and Schmidt level, respectively.

However, since the Schmitt level depends on the power supply voltage and is also affected by the temperature characteristics of the base-emitter voltage of the transistor 16 and 20, it is not possible to set a wide power supply voltage range, and the Schmitt level setting depends on the power supply voltage. It had drawbacks such as fluctuation.

This invention has been made in view of the above-mentioned drawbacks, and provides a signal detection circuit in which the signal detection level and the time limit setting for the no-time signal state do not change due to the influence of power supply voltage, etc., and in which the time limit setting is easy. It is.

Hereinafter, this invention will be explained in detail using FIGS. 3 and 4.

FIG. 3 is a block diagram showing an embodiment of the configuration of the present invention, and in the figure, numerals 1 to 3 are the same as those in FIG. 1.

6 is a switch circuit, and 7 is a delay circuit.

In this configuration, the switch circuit 6 is turned on and off depending on the level of the rectified voltage.

When the switch circuit 6 is turned off with no signal, the delay circuit 7
works and gets the output.

In Figure 4, the rectifier circuit consists of a diode 13 and a capacitor 14.
, a resistor 15, and a transistor 22 as a switch circuit.

Further, the delay circuit includes a resistor 23, a capacitor 24, and a voltage comparator 25.

In the signal state, the rectified voltage is high and the transistor 22 is turned on, so the capacitor 24 is discharged and the output terminal 5G
It becomes t'low.

When the transistor 22 is turned off in a no-signal state, the capacitor 24 is discharged through the resistor 23, and when it exceeds the voltage comparator reference voltage 2, ef, the output voltage at the output terminal 5 is inverted.

This delay time td is expressed by the following equation.

However, R and C are the values of the resistor 23 and capacitor 24.

Further, when the state changes from a no-signal state to a signal state, the transistor 22 is turned on and the output is instantaneously inverted.

Here, if the reference voltage ■ref depends on the power supply voltage ■,
That is, when ■ref-αV (α is a ratio constant), the previous delay time td becomes td = -RCln (1-a), and the resistance 2
3 capacitor 24.

Therefore, there is no influence of the power supply voltage (2), the power supply voltage range can be widened, and the no-signal state time td can be easily set.

Further, the signal level can also be set corresponding to the on/off level of the switch circuit 5 based on the rectified voltage.

As explained above, this invention uses a delay circuit to detect the no-signal state of the signal source, so it has the advantage that the time limit setting is less likely to fluctuate due to the influence of the power supply voltage, and the time limit setting is easy. have

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an example of a conventional signal detection circuit.
FIG. 2 is a specific circuit diagram of FIG. 1, FIG. 3 is a block diagram showing an embodiment of the signal detection circuit of the present invention, and FIG. 4 is a circuit diagram showing a specific embodiment of FIG. 3. It is. In the figure, 3 is a rectifier circuit, 6 is a switch circuit, and 7 is a delay circuit. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Claims] 1. A rectifier circuit that generates a rectified voltage according to a signal from a signal source; a switch circuit that performs switching according to the rectified voltage of this rectifier circuit; 1. A signal detection circuit comprising a delay circuit that obtains an output signal when a no-signal state continues.