JP2552693B2 - Monostable multivibrator - Google Patents

Description

The present invention relates to a multivibrator suitable for timing adjustment in a tracking adjustment circuit of a video tape recorder.

[Conventional technology]

A tracking servo is installed in the video tape recorder, and FIG. 4 shows a conventional tracking adjustment circuit in this tracking servo.

This tracking adjustment circuit has a tracking servo.
It has a main circuit inside IC2 and a variable resistor 4,
A monostable multivibrator (MM) 14 in which a time constant circuit 10 composed of 6 and a capacitor 8 is connected to a time constant setting terminal (CR terminal) 12 and a ground terminal 13 is installed. A voltage common to the power supply voltage V _D applied to the power supply terminal 16 on the main circuit side of the MM 14 is used for the time constant circuit 10, and the capacitor 8 is charged through the variable resistors 4 and 6. The charging / discharging of the capacitor 8 is performed in response to the trigger signal TP from the pulse generator 18 as a synchronous reference oscillator, which is applied to the MM 14. As a result, the tracking adjustment pulse MP depending on the trigger signal TP and the charge / discharge time constant of the capacitor 8 is MM14.
Obtained from

The pulse MP obtained from this MM14 is applied to the capstan phase comparator 20 and compared in phase with the reproduction control pulse CP. A tracking adjustment signal DP is obtained by this phase comparison and is used as a control input of a capstan motor (not shown).

Therefore, in such a tracking adjustment circuit,
The midpoint adjustment is set and set by the variable resistor 4, and arbitrary tracking adjustment is performed by the variable resistor 6. The tracking constant is adjusted by adjusting the time constant of the time constant circuit 10 with the variable resistors 4 and 6.

FIG. 5 shows a conventional monostable multivibrator used in the MM14 of the tracking adjustment circuit.

A discharge circuit 22 is installed in the capacitor 8, and a field effect transistor (hereinafter referred to as FET) 24 of the discharge circuit 22 is synchronized with the leading edge of the trigger signal TP shown in FIG. Then, it becomes conductive, the capacitor 8 is discharged in the pulse width tp section of the trigger signal TP, and the FET 24 is cut off at the trailing edge of the trigger signal TP.

When the FET 24 is cut off, the capacitor 8 passes through the variable resistors 4 and 6, and as shown in FIG.
It is charged with a time constant determined by the combined resistance value R of 6 and the capacitance C of the capacitor 8.

The charging voltage V _CR of the capacitor 8 is applied to the comparator 26 through the CR terminal 12, and the threshold voltage V _th as a reference voltage set by dividing the power supply voltage V _D by the resistance ratio of the resistors 28 and 30. Compared to. This comparison result is taken out as a differential output, and the comparison output EP is obtained through the inverter 32. In this case, as shown in C of FIG. 6, the comparison output EP is the capacitor 8 shown in B of FIG.
Is a pulse that becomes a high (H) level in a section in which the charging voltage V _CR of the above exceeds the threshold voltage V _th .

The comparison output EP and the trigger signal TP are applied to the AND circuit 34 to take the logical product to obtain the output pulse MP shown in D of FIG. 6, and the capstan phase comparator shown in FIG.
Added to 20.

[Problems to be Solved by the Invention] By the way, in the tracking adjustment circuit using such a monostable multivibrator, when the charging voltage V _CR of the capacitor 8 exceeds the threshold voltage V _th , the output of the MM14 (output pulse MP) Is reversed, but in such an operation, CR
In order to know the end of the time period because the potential of the terminal 12 does not change, an output test terminal 36 is provided as shown in FIG. 4, and the end of the time period is output from the output test terminal 36 of the MM14. Therefore, the number of terminals will increase when integrated into an IC.

Therefore, the present invention allows the end of the time period to be confirmed on the time constant setting terminal side.

[Means for solving the problem]

The monostable multivibrator of the present invention is a monostable multivibrator incorporated in (2) as illustrated in FIG. 1, wherein a capacitor (8) charged through a resistor (4) is used when the IC is used. A time constant circuit (10) connected to the constant setting terminal (12), and the charging voltage of the capacitor of this time constant circuit is applied to the time constant setting terminal, and the charging voltage and the reference voltage are compared, A comparator (26) that generates an output indicating that the charging voltage has reached the reference voltage and a discharging circuit (22) that is connected in parallel with the capacitor of the time constant circuit and discharges the capacitor when the capacitor is conductive. And a switching element (FET 24) that forms a trigger signal, and receives the trigger signal and the output of the comparator, the leading edge of the trigger signal or the output of the comparator. A logic circuit (40) in which the capacitor is brought into a discharging state by making the switching element conductive, and the switching element is brought into a cutoff state by the trailing edge of the trigger signal to stop the discharging of the capacitor into a charging state. And the end of the time period can be confirmed through the voltage of the time constant setting terminal.

[Action]

The arrival of the leading edge of the trigger signal TP causes the switching element (FET 24) to become conductive through the logic circuit 40, and the conductive state is maintained until the arrival of the trailing edge of the trigger signal TP.
The capacitor 8 is discharged in the conduction section of the switching element (FET 24), and the capacitor 8 is set to the initial state.

When the trailing edge of the trigger signal TP arrives, the switching element (FET2
When 4) shifts to the cutoff state, the capacitor 8 is charged through the resistors (variable resistors 4 and 6), and the charging voltage V _CR rises with a time constant τ determined by the resistance value of the resistor and the capacitance of the capacitor 8.

When the charging voltage V _{CR of the} capacitor 8 shifts to the reference voltage (threshold voltage V _th ), the output of the comparator 26 is inverted, and in response to this output inversion, the logic circuit 40 shifts the switching element (FET 24) to the conductive state. Then, the capacitor 8 is discharged.

In such a multivibrator, the start point and the end point of the time period are determined by the transition of the switching element (FET 24) from the cut-off state to the conductive state, which can be seen from the transition of the voltage on the capacitor 8 side.

〔Example〕

FIG. 1 shows a tracking adjustment circuit which is an embodiment of the monostable multivibrator of the present invention.

In the monostable multivibrator, a time constant circuit 10 is installed outside the main circuit section inside the tracking IC 2 as well as outside.

The time constant circuit 10 includes variable resistors 4 and 6 and a capacitor 8
The resistance values of the variable resistors 4 and 6 are set to be large in the former case, and are used for reference setting such as adjustment at the time of shipment, and are semi-fixed. The charging voltage V _CR of the capacitor 8 charged through the variable resistors 4 and 6 is applied to the comparator 26 through the time constant setting terminal (CR terminal) 12 and compared with the threshold voltage V _th as a reference voltage. The comparator 26 includes a differential circuit composed of a pair of FETs 261 and 262. The gate of the FET 261 has a charging voltage V _CR , and the gate of the FET 262 has a threshold voltage V _th from a voltage dividing circuit by resistors 28 and 30.
In addition, a constant current is supplied as an operating current from the FET 263 forming a constant current source and the resistor 264 to the FETs 261 and 262 through the FET 265. Therefore, the charging voltage
As long as V _CR does not exceed the threshold voltage V _th , FET2
61 is conductive, FET 262 remains off, charging voltage V
_{When CR} exceeds the threshold voltage V _th , the FET 261 shifts to the cutoff state and the FET 262 shifts to the conductive state. The differential output obtained by such switching operation is
It is taken out through a current mirror circuit composed of FETs 266 and 267 and added to the gate of FET 268. FET268, FET263
And FET269 that forms a current mirror circuit are connected in series, and the charging voltage V
A comparison output EP between _CR and the threshold voltage V _th is taken out and output through the FETs 321 and 322 of the inverter 32.

The output EP of the comparator 26 is added to the logic circuit 40 side,
After being inverted by the inverter 401, it becomes the set input of the flip-flop (FF) circuit 402. This FF circuit 402
The non-inverted output Q is applied to the NAND circuit 403, and the inverted output is applied to the OR circuit 404 and, after being inverted through the inverter 405, becomes the set input of the FF circuit 406.

A trigger signal TP is applied to the NAND circuit 403 and the OR circuit 404 from the pulse generator 18 as a reference oscillator.
Therefore, in the NAND circuit 403, the NAND condition is satisfied by the non-inverted output Q of the FF circuit 402, the inverted output of the FF circuit 406 and the trigger signal TP, and in the OR circuit 404, the inverted output of the FF circuit 402 and the trigger signal TP. OR condition is satisfied.

The tracking servo IC2 is connected to the capacitor 8.
FET2 as a switching element installed on the main circuit side of
A discharge circuit 22 consisting of 4 and a resistor 25 is added. F
To the gate of ET24, the logic output of the logic circuit 40 based on the output inversion of the comparator 26 and the trigger signal TP are applied through the OR circuit 404, and the FET 24 is turned on by the logic output of the logic circuit 40 and the trigger signal TP. Is established.

Then, when the trigger signal TP shown in FIG. 2A is applied from the pulse generator 18, the FET 24 becomes conductive at its leading edge and its conductive state continues to its trailing edge. That is, the FET 24 conducts during the pulse width tp of the trigger signal TP, and the capacitor 8
Is discharged, and the capacitor 8 is in the initial state.

When the FET 24 shifts to the cutoff state at the trailing edge of the trigger signal TP, the capacitor 8 is charged through the variable resistors 4 and 6 as shown in B of FIG. Charging voltage V of capacitor 8
_{When CR} reaches the threshold voltage V _th , the comparator 26 causes the output inversion and the low (L) level output. When this output is applied to the FF circuit 402 through the inverter 401,
The inverted output of the FF circuit 402 becomes the L output, and the H output is added to the gate of the FET 24 through the OR circuit 404.
As a result, the FET 24 becomes conductive and the capacitor 8 is discharged through the FET 24 and the resistor 25. Therefore, as shown in FIG. 2C, the output pulse MP as the tracking adjustment output is obtained from the OR circuit 404 and applied to the capstan phase comparator 20.

In this case, the pulse width of the output pulse MP can be arbitrarily set by adjusting the variable resistors 4 and 6 to change the magnitude of the time constant τ from the relationship with the threshold voltage V _th .

When the time constant τ is made extremely large, A in FIG.
As shown in B and B, even if the trigger signal TP is given,
Charge voltage of the capacitor 8 within the time interval T of the trigger signal TP
The FET 24 becomes conductive due to the arrival of the trigger signal TP before V _CR shifts to the threshold voltage V _th .
The output pulse MP shown in C of the figure is obtained. That is, in the conventional monostable multivibrator, the trigger signal TP is applied until the charging voltage V _CR of the capacitor 8 reaches the threshold voltage V _th.
In this monostable multivibrator, the FET 24 is turned on by the trigger signal TP, and the output pulse MP shown in C of FIG. 3 is obtained.

Also, as is clear from the operation shown in FIG. 2B, CR
Since the discharge path is formed in the terminal 12, it is possible to know the end of the time period by detecting the potential of the CR terminal 12, so a separate terminal for detecting the output of the conventional multivibrator is provided. No need.

Then, while monitoring the end point of such a time limit, the center value in the tracking adjustment is adjusted by the variable resistor 4, and the fine adjustment can be performed by the variable resistor 6 in the tracking adjustment as the video tape recorder.

In the embodiments, the tracking adjustment circuit has been described as an example, but the monostable multivibrator of the present invention can be used in various cases installed inside the IC.

〔The invention's effect〕

As described above, according to the present invention, when the time constant is increased, the capacitor of the time constant circuit causes the switching element to conduct and discharge due to the trigger signal, so that an output pulse corresponding to the trigger signal is generated and the trigger signal is generated. It is possible to know the end of the time limit through the time constant setting terminal side connected to the time constant circuit without causing the frequency division of
When integrated into an IC, it is not necessary to provide a separate test terminal to know the end of the time limit.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing a tracking adjustment circuit which is an embodiment of the monostable multivibrator of the present invention, and FIGS. 2 and 3 show the operation of the monostable multivibrator in the tracking adjustment circuit shown in FIG. 4 and 5 are block diagrams showing the tracking adjustment circuit, and FIG.
FIG. 6 is a circuit diagram showing a monostable multivibrator in the tracking adjustment circuit shown in FIG. 6, and FIG. 6 is a diagram showing an operation of the monostable multivibrator shown in FIG. 4, 6 ...... Variable resistance 8 ...... Capacitor 10 ...... Time constant circuit 22 ...... Discharge circuit 24 ...... FET (switching element) 26 …… Comparator 40 …… Logic circuit

Claims (1)

(57) [Claims] 1. A monostable multivibrator incorporated in an IC, comprising a time constant circuit formed by connecting a capacitor charged through a resistor to a time constant setting terminal of the IC, and the capacitor of the time constant circuit. A charging voltage is applied to the time constant setting terminal, compares the charging voltage and a reference voltage, and generates an output indicating that the charging voltage has reached the reference voltage, and a comparator of the time constant circuit. A switching element that is connected in parallel with the capacitor and that constitutes a discharge circuit that discharges the capacitor when the capacitor is conducting; a trigger signal and the output of the comparator; and a leading edge of the trigger signal, or By making the switching element conductive by the output of the comparator, the capacitor is brought into a discharging state, and a trailing edge of the trigger signal is generated. A logic circuit that stops the discharge of the capacitor and shifts to a charging state by shifting the switching element to a cutoff state, and it is possible to confirm the end of the time period through the voltage of the time constant setting terminal. Characteristic monostable multivibrator.