JPS5942780Y2 - transistor circuit device - Google Patents

Description

[Detailed description of the invention] The present invention is a transistor circuit device, particularly an integrated circuit (hereinafter referred to as IC) for a video signal processing circuit of a television receiver.
It is related to.

FIG. 1 shows a conventionally used circuit configuration.

In the figure, 1 is a tuner, 2 is a video intermediate frequency amplification circuit (hereinafter referred to as VIP circuit), and 3 is a second video detection circuit (
4 is an automatic gain control circuit (hereinafter referred to as an AGC circuit), 5 is a synchronous separation circuit, and 6 is a noise cancellation circuit.

The part surrounded by the dotted line is the IC circuit; T is a transistor that constitutes an emitter follower circuit connected to the second video detection circuit 3, which outputs a composite video signal with a lower impedance than the emitter and adds it to the synchronous separation circuit 5. .

The synchronous separation circuit 5 is of a self-biasing type, and time constant circuits 51, 52, 53, and 54 for self-biasing are connected to the base circuit.

55 is a sync separation transistor which separates and extracts a sync signal from the composite video signal applied to the base.

A switching transistor 62 is connected between the emitter of the synchronous separation transistor 55 and the power supply vccO.

This switching transistor 62 corresponds to the output gate stage of the noise cancellation circuit 6, and the noise signal detection circuit 61
controlled by the output of

That is, when there is no external noise, the switching transistor 6
2 is in a saturated state, and when external noise enters, the switching transistor 62 is controlled to be in a cut-off state to prevent the synchronization separation operation from being disturbed by external noise.

On the other hand, the output signal of the noise signal detection circuit 61 is
When external noise enters, the operation of the AGC circuit 4 is stopped, or the noise of the input signal is suppressed by adding noise with the opposite phase to the noise component of the input signal of the AGC circuit 4.
The operation of the GC circuit 4 is prevented from being disturbed by noise.

Now, consider the synchronous separation operation using the circuit configuration shown in FIG.

When external noise enters, the switching transistor 62 is turned off, the synchronous separation transistor 55 is also turned off, the synchronous separation operation is stopped, and the external noise does not appear in the synchronous separation output.

However, when external noise enters, the base bias resistance is 56.5
A charging current due to noise flows through the time constant circuit 51, 52.5354 through 7, and the capacitor 51.53 is overcharged.The noise disappears, the switching transistor 62 becomes saturated, and the synchronous isolation transistor 550 circuit becomes normal. Even if the circuit connection is made to operate normally, the capacitor 51.5
In the trench where the overcharged noise current discharges in step 3, the base bias of the synchronous separation transistor 55 becomes a bias in the cutoff direction, and the synchronous separation output does not appear or the waveform of the synchronous separation output does not become a normal voltage waveform. This caused problems such as synchronization being disrupted and video being distorted.

On the other hand, consider a case where no external noise is introduced.

In this case, the switching transistor 62 is in a saturated state, and although the synchronous separation operation is performed normally,
The saturation resistance of the switching transistor 62 is connected between the emitter of the synchronous separation transistor 55 and the power supply Vce, and this saturation resistance causes the following inconvenience in the synchronous separation operation.

FIG. 2 shows the equivalent circuit in this case, and FIG. 3 shows an explanatory diagram of its operation.

63 in FIG. 2 is the saturation resistance of the switching transistor 62.

In Figure 3, the horizontal axis is the base voltage VB, and the vertical axis is the collector current I.
FIG. 4 is a diagram showing the operating characteristics of the synchronous separation stage when c is taken.

A is a case where there is no saturation resistor 63, and an opening is a case where there is a saturation resistor 63, and compared to A, a larger base voltage is required to flow the same collector current.

The waveform shown at the bottom of FIG. 3 is the base input voltage waveform, and the waveform shown at the right is the collector output waveform.

Considering the operation of the characteristics of A, the base bias BL should be selected with the base bias resistors 56 and 57 so that the synchronization separation transistor 55 is saturated at the peak of the synchronization signal of the base input composite video signal. A collector output signal icm appears for b1, and only the synchronization signal is separated.

On the other hand, considering the operation of the mouth characteristics, the base bias ■b2 is set so that the synchronization separation transistor 55 is saturated at the peak of the synchronization signal of the base input composite video signal, as described above.
When selecting , the collector output signal ic2 appears in response to the base input signal b2, but as shown in the figure, complete synchronization separation operation is not performed with the same base input signal as in case A, and the pedestal section and the video section This will disrupt synchronized operation.

To prevent this, you can increase the base input composite video signal, but the electric field strength will become smaller and below a certain level (
(below the level at which the VIP and AGC circuits that control the VIP circuit operate), the composite video signal becomes small, causing the above-mentioned problems.

That is, the emitter circuit of the synchronous separation stage has an impedance of l
A better synchronization separation operation is achieved when the switching transistor 62 as shown in FIG.
It is not good to connect and die.

On the other hand, when viewed as an IC circuit, it is necessary to reduce the number of pins as much as possible in order to accommodate many functions in the same package and keep the price low.

Therefore, it is necessary to configure the circuit so that the number of pins is as small as possible.

The circuit configuration of the present invention eliminates these inconveniences and problems.

An embodiment of the circuit configuration of the present invention is shown in FIG.

The same blocks and elements as in FIG. 1 are given the same reference numerals.

The difference between FIG. 1 and FIG. 4 is that a circuit of an emitter follower transistor 8 having a polarity opposite to that of the transistor 7 is connected to the front stage of the emitter follower transistor in FIG. Noise cancellation circuit 6
The noise-cancelled signal appears at the emitter B terminal of the transistor 7, and the signal is supplied from the B terminal to the synchronous separation circuit 5 and the AGC circuit 4.

Here, to explain the operation of noise removal, the peak value of the synchronization signal of a composite video signal containing noise is set as a reference level, and there is a means for detecting noise that is higher than the reference level, and a means for detecting high-frequency spike-like noise signals. The above-mentioned noise canceling circuit 6 is a noise signal detection circuit equipped with one or both of means for
1 included in the composite video signal from this noise canceling circuit 6.
outputs a detected noise signal that is in opposite phase to the input noise signal.

At the base of Transin Tough, the noise signal is removed by superimposing it on the original composite video signal containing noise.

In this way, there is no need to use the switching transistor 62 as shown in FIG. 1, there is no inconvenience as mentioned above, and the synchronization separation operation is not disturbed by external noise.

Furthermore, the noise canceling circuit (for example, a circuit corresponding to the switching transistor 62 of the synchronous separation circuit) as described in the case of FIG. 1 is not required at all in the AGC circuit 4, and the circuit configuration is simplified.

On the other hand, considering the DC level of the input signal to the AGC circuit 4, in the case of Fig. 1 it is taken out directly from the output point of the second video detection circuit 3, but in the case of Fig. 4 it is taken out directly from the output point of the second video detection circuit 3, but in the case of Fig. 7.9, but transistor 7.
The base-emitter voltages of 8 are almost the same and compensate each other, and the potential at point B and the voltage at point A are almost the same, so the DC potential of the second video detection output is immediately converted to the DC voltage at point B. It can be seen as a rank.

In the case of Figure 4, the IC circuit part is also surrounded by a dotted line, but as can be seen from the comparison with Figure 1, the number of pins has decreased by 1 to 2.
-[, this circuit is suitable for an IC circuit (there is no D terminal in the case of FIG. 1), and it can be multifunctional when using the same package compared to the case of FIG.

In other words, according to the configuration of the present invention, the number of terminals required is small when considering an IC circuit, and therefore, when making a circuit IC with the same function in a package with the same number of terminals, the number of terminals used is smaller than in the conventional example. As a result, the remaining terminals can be used to incorporate circuits with other functions into the IC, resulting in so-called multifunctionality.

Furthermore, in the present invention, by reducing the number of pins, the price can be lowered.

Another embodiment of the invention is shown in FIG.

However, FIG. 5 only shows the main features of the circuit of the present invention.

In the case of FIG. 5, only the positions of transistors 7 and 8 in FIG. 4 are exchanged, but the operation and function are exactly the same.

FIG. 6 shows the main parts of another embodiment of the present invention.

Figure 6 shows the transistors 8 and 8' of the emitter follower on the input side connected to Darlington in order to increase the input impedance. In this case, the emitter follower 7 and 7' of the subsequent stage are also connected to Darlington. This is exactly the same as in the above embodiment.

FIG. 7 shows still another embodiment of the present invention.

Figure 7 shows how n transistors with the same polarity (for example, an NPN transistor) are connected between the A terminal and the B terminal as an emitter follower circuit, and n transistors with the opposite polarity (for example, a PNP transistor) are connected as an emitter follower circuit. Connected as a circuit, the input signal of the noise canceling circuit 6 is taken out from the input end of these emitter follower circuits, or from an arbitrary point between the input end and the output end if necessary, and the input signal is taken out from the circuit 9. 2n that adds a noise cancellation signal to any point in the latter stage to remove external noise signals.
This is the case for a stage emitter follower circuit.

This circuit also operates in the same way as the circuit shown in FIG. 4 and has the same features.

By adopting the configuration of the present invention as described above, it is possible to obtain a circuit with a simplified configuration that can eliminate problems when external noise does not enter, and can also prevent disturbance of synchronization separation operation due to external noise. be able to.

Furthermore, when integrated into an IC, the number of pins is reduced, the structure can be made at low cost, and it has the advantage of being easily multifunctional.

Further, according to the present invention, the video signal from which the noise has been removed can maintain the DC level of the detection output and provide a signal with low output impedance, and the output signal from the second transistor can be transferred to the IAGc circuit. It can also be supplied to a synchronous separation circuit to obtain good operating characteristics.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional transistor circuit, Figure 2 is an equivalent circuit diagram of the main part of Figure 1, Figure 3 is an explanatory diagram of the operation of the circuit in Figure 2, and Figure 4 is an example of the present invention. The circuit diagrams of the transistor circuit device according to the embodiment, FIGS. 5, 6, and 7 are main part circuit diagrams showing other embodiments of the present invention. 3...Second video detection circuit, 4...Automatic gain control circuit, °5...Synchronization separation circuit, 6...
...Noise cancellation circuit, 7.8...Transistor.

Claims (1)

[Scope of utility model registration request] A first transistor is connected as an emitter follower circuit to a first video detection output circuit of a television receiver, and a second transistor having a polarity opposite to that of the first transistor is connected to an emitter output terminal of this circuit as an emitter follower circuit. , an input signal to a noise canceling circuit is supplied from the base circuit of the first transistor, a noise signal is detected by this noise canceling circuit, and a noise signal having a polarity opposite to that of the noise signal applied to the input terminal of this noise canceling circuit is sent to its output terminal. The noise signal is taken out and added to the base circuit of the second transistor so as to cancel out the noise signals, and a synchronization isolation transistor consisting of a synchronization isolation transistor and a time constant circuit inserted in the base circuit of this transistor is provided. circuit, and an automatic gain control circuit, the noise-removed composite video signal is transmitted from the emitter output terminal of the second transistor to the base of the synchronous separation transistor via a time constant circuit, and the automatic gain control circuit. Add the deceased directly to the above-mentioned 1. A transistor circuit device characterized in that a second transistor, a noise canceling circuit, and a synchronous separation circuit excluding the time constant circuit are integrated on one substrate.