JPH0149206B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to an amplitude limiting circuit, generally called a white dark clip circuit, used in television receivers and VTRs, and particularly provides a circuit configuration optimal for semiconductor integrated circuits. It is something to do.

[Prior art]

Conventionally, there has been a device of this type as shown in FIG. In the figure, 1 is an input terminal, 2 is a bias terminal, 3 and 4 are voltage application terminals, 5 is an output terminal,
6 is a power supply, 7, 8, 9 are pnp transistors, 1
0 and 11 are npn transistors, 12 to 15 are resistors, and 16 and 17 are variable voltage sources.

FIG. 2 is a diagram showing an example of waveforms used to explain the conventional example. In the diagram, a is the input waveform, that is, the base waveform of the transistor 7, b is the base waveform of the transistor 10, and c is the output waveform.

The following operation will be explained.

In FIG. 1, a signal input from an input terminal 1 is guided to a differential circuit composed of pnp transistors 7 and 8. The base potential of the transistor 8, that is, the potential of the control voltage application terminal 3 is set in advance by the voltage source 1.
6, the potential is set to be an appropriate amount higher than the base potential of the transistor 7.

Now, if the waveform shown in Figure 2a is input to the base of transistor 7, the signal will be transmitted to the base of transistor 10 only during the period when the potential is lower than the base potential V8b of transistor 8, as shown in Figure 2b. The high potential side is amplitude limited. Further, the signal is guided to a differential circuit composed of npn transistors 10 and 11. The base potential V11b of the transistor 11 is set in advance by the voltage source 17.
The potential is set to be an appropriate amount lower than the base potential of the transistor 10, and when the waveform shown in FIG. As a result, as shown in FIG. 2c, the amplitude of the low potential side is limited.

By arbitrarily setting the voltage sources 16 and 17 in this way, it is possible to limit the amplitude of the high potential side and low potential side of the input signal waveform.

Conventional amplitude limiting circuits are configured as described above, so when implementing semiconductor integrated circuits, a voltage source that limits the amplitude on the high potential side and a voltage source that limits the amplitude on the low potential side are required. Another drawback was that it was difficult to set the potential of each voltage source.

[Summary of the invention]

This invention was made in order to eliminate the drawbacks of the conventional ones as described above, and by adding an amplitude control voltage generation circuit that generates two control voltages with different polarities using a differential circuit, the input signal can be The amplitude limiting circuit can limit the amplitude of both the high potential side and the low potential side using one voltage source, reducing the number of terminals, and easily controlling the amplitude limiting. is intended to provide.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings. In FIG. 3, 40 is an amplitude control voltage generation circuit that generates two amplitude control voltages from one type of input voltage, and in this circuit 40, 101 is an input terminal, 102 is a bias terminal, 20 is an npn transistor 131, 132, resistance 118, 119,
112, 120 and a constant current source 129; 30 is an npn transistor 133;
134, a second differential circuit consisting of resistors 123, 124, 121, 125 and a constant current source 130, 1
26 is a resistor which is a load of the first differential circuit 20;
27 and 128 are two resistors serving as loads for the second differential circuit 30, 122 is a resistor, 135 is an amplitude limit control terminal, and 136 is an external variable resistor for setting the amplitude limit level. Further, 50 indicates the amplitude control voltage generating circuit 40 according to the control voltage of the amplitude control voltage generating circuit 40.
This is an amplitude limiting circuit main body that limits the amplitude of a waveform whose input signal waveform is level-shifted by the first differential circuit 20. In the circuit 50, 107, 108, 109 are pnp transistors, 110, 111 is an npn transistor, 11
3, 114, 115 are resistors, 105 is an output terminal,
106 is a power terminal.

Next, the operation will be explained.

A signal input from the input terminal 101 is guided to the first differential circuit 20 composed of npn transistors 131 and 132. Then, due to the level shift operation within the differential circuit 20, the amplitude limiting circuit main body 50
A DC level-shifted version of the input signal waveform is introduced to the base of the transistor 107 inside. On the other hand, the second differential circuit 30 composed of the pnp transistors 133 and 134 is the same as the differential circuit 2 composed of the aforementioned transistors 131 and 132.
Circuit constants similar to 0 (resistance value R112=R110=R121
= R125, resistance value R118 = R119 = R123 = R124, resistance value R126 = R127 = R128, constant current source current value I129
= I130), and by varying the external variable resistor 136, the base potential of the transistor 133 forming the differential circuit 30 is changed, and the current flowing through the transistors 133 and 134 is controlled,
Transistors 108 and 11 that perform amplitude limiting operation
The base potential of 1 can be determined arbitrarily.

The operation will be explained below for each setting condition of the external variable resistor 136.

() Condition When the resistance value of the external variable resistor 136 is infinite (see Figure 4) In this case, the base potentials of the transistors 133 and 134 are the same potential, and the current of the constant current source 130 is equally divided into each. , transistor 10
The base potential V108b of transistor 8 and the base potential of transistor 109 are the same potential. Furthermore, this potential is also the same as the base potential of the transistor 107. Transistor 109 is transistor 107
and 108 to similarly compensate for the DC level shift of transistors 110 and 108.
The base potential of the transistor 111 and the base potential V111b of the transistor 111 are configured to be the same potential. As a result, no signal waveform is output to the output terminal 105 as shown in FIG. 4c.

() Conditions When the resistance value of the external variable resistor 136 is zero (amplitude limit control terminal 135 is grounded) (see Fig. 5), the base potential of the transistor 133 is equal to the voltage at the bias terminal 102 between the resistor 121 and the resistor 121.
22, and the ratio of currents flowing through transistors 133 and 134 changes. Therefore, the base potential V108b of the transistor 108 is higher than that under the condition, and the base potential V111b of the transistor 111 is lower than that under the condition. As a result, the input signal waveform is output as is to the output terminal 105 as shown in FIG. 5c.

() Conditions When the resistance value of the external variable resistor 136 is arbitrarily set (see Figure 6), in this case, the base potential of the transistor 133 is the same as the voltage at the bias terminal 102 between the resistors 121 and 1.
22 and the variable resistor 136.
The base potentials V108 and V111b of V108 and V111b are intermediate between the above conditions, and by setting the variable resistor 136 arbitrarily, the same operation as that described in the conventional example is performed, and the high potential side and A waveform whose amplitude is limited on the low potential side is output to the output terminal 105 as shown in FIG. 6c. Another feature is that the high potential side amplitude and the low potential side amplitude change with the same amplitude.

In this way, in this embodiment, the external variable resistor 13
6, the amplitude limit control terminal 13
By changing the DC potential of transistors 133 and 5,
Controls the current flowing through the differential circuit consisting of 134,
The base potentials of the transistors 108 and 111 that perform amplitude limitation are arbitrarily determined, and 1
By varying the variable resistor connected to the two terminals, it is possible to simultaneously limit the amplitude of the high potential side and the low potential side of the input signal waveform.

Note that in the above embodiment, the external variable resistor 136
The case where the external variable resistor 13 is inserted between the amplitude limit control terminal 135 and the ground has been explained.
6 is inserted between the amplitude limit control terminal 135 and the power supply,
Furthermore, the base potential of the transistor 108 may be supplied from the collector of the transistor 134, and the base potential of the transistor 109 may be supplied from the collector of the transistor 133, and it goes without saying that the same effects as in the above embodiment can be expected.

〔Effect of the invention〕

As described above, according to the present invention, since the amplitude control voltage generation circuit that generates two control voltages with different polarities is added using a differential circuit, the number of terminals can be reduced. This has the advantage that amplitude limit control can be easily performed and a circuit configuration suitable for semiconductor integrated circuits can be obtained.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing an embodiment of a conventional amplitude limiting circuit, FIG. 2 is a signal waveform diagram of the circuit in FIG. 1, and FIG. 3 is a block diagram showing an amplitude limiting circuit according to an embodiment of the present invention. , FIGS. 4 to 6 are waveform diagrams showing signal waveforms of the circuit of FIG. 3 according to setting conditions of the external variable resistor of FIG. 3. 40... Amplitude control voltage generation circuit, 20, 30...
...first and second differential circuits, 126...resistor (first
load), 127, 128... Resistor (second load), 131, 132, 133, 134... Transistor, 118, 119, 123, 124...
Resistor, 112, 120, 121, 125... Resistor, 129, 130... Constant current source, 101... Input terminal, 102... Bias terminal, 135... Amplitude limit control terminal, 136... Variable resistor, 106
...Power supply terminal, 50...Amplitude limiting circuit body.

Claims (1)

[Claims] 1 An amplitude limiting circuit that limits the amplitude of a high potential side and a low potential side of an input signal waveform, in which a resistor is connected to the emitters of a pair of transistors, the other ends of the resistors are commonly connected, and the common connection A constant current source is connected to the point, a resistor is connected to the base of each of the pair of transistors, the other ends of the resistors are commonly connected, and the same bias power source is connected to the common connection point. 1, a second differential circuit, an input terminal for applying an input signal to the base of one transistor serving as one input terminal of the first differential circuit;
a first load for extracting a signal level-shifted by the differential circuit; an amplitude limiting control terminal connected to the base of one transistor serving as one input terminal of the second differential circuit; , a variable resistor inserted between the amplitude limiting control terminal and a power source or ground, and two second loads that take out two DC control voltages with different polarities from the second differential circuit. The present invention is characterized by comprising: an amplitude control voltage generation circuit; and an amplitude limiting circuit main body that limits the amplitude of a signal taken out by the first load according to two control voltages taken out by the second load. Amplitude limiting circuit.