JPH09148848A - Broadband signal transmission circuit and amplifier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To lower the source voltage of the signal transmission circuit and save the electric power and space for AV equipment, etc., by setting the output potential of an amplifier in the absence of a signal a specific value less than a reference potential. SOLUTION: The broadband signal transmission circuit 101 consists of a broadband amplifier 1 and terminating resistances R4 and R5. The broadband amplifier 1 is so constituted as to operate with a single power source of 3V and generate an output potential which is <=0.5V lower than the reference potential in the absence of a signal. As the resistances R4 and R5 for termination, resistances of 75Ω are used so as to generate impedance matching conditions of 75Ω. The output of the broadband amplifier 1 is connected directly to those resistances R4 and R5 for termination not through a coupling capacitor. The resistances R4 and R5 are connected in series between the output of the amplifier 1 and the reference potential and a video signal take out with impedance of 75Ω at their intermediate connection point is sent to another AV equipment through a connection cable.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband signal transmission circuit, and more particularly to a technique effective when applied to a circuit for transmitting a video signal between AV equipments (Audio-Visual). The present invention relates to a technique effectively used for a power-saving and space-saving portable AV device that operates at a low power supply voltage of 3V.

[0002]

2. Description of the Related Art For example, home video cameras and VTs
AV equipment such as R (video tape recorder),
A wideband signal that sends out a composite video signal having a very wide frequency band from low frequency to high frequency with a constant impedance (75Ω) and an amplitude level (1.0 Vpp) in order to exchange it between AV equipment. A transmission circuit is provided for each device.

Conventionally, in this kind of wide band signal transmission circuit,
As shown in FIG. 7, a wide band amplifier 1 operating with a single power supply having a standard power supply voltage Vcc (5 V) amplifies a video signal,
The amplified output has been passed through a DC-coupling coupling capacitor Co, terminated by resistors R4 and R5, and then sent out to a cable. The tip of the cable is connected to the video input terminal of another AV device.

Here, the reason for terminating with the resistors R4 and R5 is to perform impedance matching with the transmission line. T
For video signal transmission to be input to AV equipment such as V, an amplitude level of 1.0 Vpp with an impedance of 75Ω is generally standard. Therefore, the resistors R4 and R5
Are each set to 75Ω to form their 75Ω impedance match. Further, the wide band amplifier 1 is set in gain so as to amplify the video signal up to 2.0 Vpp and output it.

The wide band amplifier 1 is composed of a kind of direct current amplifier having a SEPP (single end push pull) type output circuit, and its output signal is a power supply potential Vcc (5
C) and the reference potential (0V), which is almost the middle potential (Vcc / 2)
= About 2.5 V) is included. This DC component (2.5V) is cut off by the coupling capacitor Co, and only the video signal component (2.0Vpp) is taken out and given to the termination resistors R4 and R5.

FIG. 8 shows the output signal before the DC cut, and FIG. 9 shows the output signal after the DC cut.

As a wide band amplifier for the above wide band signal transmission circuit, for example, "Hitachi Consumer IC Data Book Video IC Edition September 1991" issued by Hitachi, Ltd.
Video switch IC “HA11810” described on page 292.
4 ”etc.

[0008]

However, it has been clarified by the present inventors that the above-described technology has the following problems.

That is, the conventional wideband signal transmission circuit has 5
It is built under a standard power supply voltage environment of V, and under a low power supply voltage environment of lower voltage such as 3 V, 75 Ω which is standard for all AV equipment such as TV.
(Impedance) /1.0 Vpp (voltage amplitude level)
It becomes impossible to send the video signal of.

The wideband amplifier 1 shown in FIG.
In order to send the Ω / 1.0 Vpp video signal, the output of the amplifier 1 must be able to obtain the 2.0 Vpp video signal.

However, for that purpose, as shown in FIG. 8, it is necessary to raise the operating power supply voltage of the wide band amplifier to nearly 5V, and at 3V, the output dynamic range (2.5V + 2) necessary to obtain the above video signal is obtained. .0
Vpp = about 4.5V) cannot be secured. On the other hand, reducing the power supply voltage from 5 V to 3 V is very advantageous in reducing power consumption and space saving by downsizing the battery.

[0012] Therefore, the present inventors consider increasing only the operating power supply of the wide band amplifier for outputting the video signal to 5V in order to realize the above-mentioned wide band signal transmission circuit under the low power supply voltage environment of 3V. did.

However, for that purpose, a booster circuit (DC-DC converter) from 3V to 5V is newly required, which hinders cost reduction and size reduction of the equipment. further,
The conversion efficiency of a DC voltage booster circuit is generally poor. Therefore, the various effects expected by setting the power supply voltage to 3 V are often canceled by the use of the booster circuit.

In the wideband signal transmission circuit described above,
Coupling for DC cut on the output of wideband amplifier 1
Although the capacitor Co is connected, a large-capacity capacitor of about 400 μ is required in order to reliably pass a wideband signal such as a video signal whose frequency component extends to the low frequency band. Since such a large-capacity capacitor Co is considerably large in size, it is especially useful for portable type A
This is a major hindrance to the miniaturization of V equipment.

Therefore, the present inventors, as shown in FIG. 10, directly connect the output of the wide band amplifier 1 to the termination resistors R4 and R5 without using the coupling capacitor Co which hinders space saving. Considered connecting.

However, in this case, since the output is not cut off from the direct current, even when there is no signal, a large direct current I from the output of the amplifier 1 to the termination resistors R4 and R5 is constantly generated.
o flows to increase power consumption. This current Io
Can be reduced by increasing the resistance value of the termination resistors R4 and R5, but the resistance value cannot be changed because it is necessary to perform impedance matching with standard 75Ω.

An object of the present invention is to reduce the power supply voltage of the wideband signal transmission circuit from 5V to 3V while ensuring the standard impedance matching condition and the standard amplitude level, thereby saving the AV equipment and the like. It is to provide a technology that enables electric power and space saving.

The above and other objects and characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings.

[0019]

SUMMARY OF THE INVENTION Among the inventions disclosed in the present application, the outline of a representative one will be briefly described.
It is as follows.

That is, when the output of the wide band amplifier operating with a single power source is terminated by a resistor and transmitted, the output potential of the amplifier in the absence of signal is set to 0.
In addition to setting it to 5 V or less, the amplified output of the amplifier is directly connected to the terminating resistor.

According to the above-mentioned means, it is possible to reduce the direct current that constantly flows from the output of the wide band amplifier to the terminating resistor, and to eliminate the need for a large-capacity coupling capacitor that hinders space saving. Amplifier 3
Even if operated under a low power supply voltage of V, it is 2.0V which is standard
The output signal of pp can be taken out without difficulty.

This makes it possible to reduce the power supply voltage of the wideband signal transmission circuit from 5V to 3V while ensuring the standard impedance matching condition and the standard amplitude level, thus saving power and space in AV equipment and the like. The purpose of enabling is achieved.

[0023]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below with reference to the drawings.

In the drawings, the same reference numerals indicate the same or corresponding parts.

FIG. 1 shows an embodiment of a wideband signal transmission circuit to which the technique of the present invention is applied.

In the figure, reference numeral 100 is an AV device such as a handy type video camera, and 101 is a wideband signal transmission circuit forming a video signal output section of the AV device 100.

The wideband signal transmission circuit 101 comprises a wideband amplifier 1 and termination resistors R4 and R5. The wide band amplifier 1 is operated by a single power source of 3V, and is configured such that the output potential when there is no signal is 0.5 V or less with respect to the reference potential (ground potential). As the termination resistors R4 and R5, 75Ω resistors are used to form an impedance matching condition of 75Ω. The output of the broadband amplifier 1 is directly connected to the terminating resistors R4 and R5 without passing through a coupling capacitor.

The terminating resistors R4 and R5 are connected in series between the output of the amplifier 1 and the reference potential, and the video signal taken out at the impedance of 75Ω from the intermediate connection point is sent to another AV device through the connection cable.

FIG. 2 shows an output waveform example of the wide band amplifier 1.

As shown in the figure, the video signal appearing at the output of the wide band amplifier 1 has an amplitude level of 2.0 Vpp which has a constant potential Vo of 0.5 V or less as a minimum level, whereby 75Ω / 1.0 Vpp. This video signal can be transmitted to another AV device. On the other hand, the output potential of the wide band amplifier 1 when there is no signal is the constant potential Vo (0.5
V or less) only.

As a result, the output dynamic range of the wide band amplifier 1 is 2.5 V or more (> 0.5 V + 2.0 Vp).
p), it is possible to obtain a video signal having an amplitude level of 2.0 Vpp necessary for transmitting a 75 Ω / 1.0 Vpp video signal. An output dynamic range of 2.5V can be easily achieved with a single 3V power supply.

Since the output potential of the wide band amplifier 1 when there is no signal becomes the above constant potential Vo (0.5 V or less), the terminating resistor R directly connected to the amplifier 1 is connected.
The DC current Io which constantly flows through the R4 and R5 is about 3 due to Io <0.5V / (75 + 75) Ω, although the resistance values of the R4 and the R5 are relatively low values of 75Ω.
It can be kept at a small current of mA or less.

As described above, the direct current I which constantly flows from the output of the wide band amplifier 1 to the termination resistors R4 and R5.
While keeping o small, it is possible to eliminate the need for large-capacity coupling capacitors that hinder space saving, and even if the amplifier 1 is operated under a low power supply voltage of 3V, a standard 2.0 Vpp signal output is provided. Can be taken out without difficulty.

As a result, it is possible to reduce the power supply voltage of the wideband signal transmission circuit 101 from 5V to 3V while ensuring the standard impedance matching condition and the standard amplitude level. Space is possible.

If the output potential of the amplifier 1 when there is no signal exceeds 0.5V, the maximum output potential of the amplifier 1 during video signal output approaches or exceeds the power supply voltage of 3V. It becomes difficult to take out the standard-compliant 2.0 Vpp output signal, and the consumption current due to the direct current Io that constantly flows through the termination resistors R4 and R5 increases when there is no signal, and the effect of the present invention is sufficient. Will not be obtained. The output dynamic range of the amplifier 1 is 3V depending on the saturation voltage of the transistor.
However, the power supply voltage of 3 V cannot be directly used as the output dynamic range.

FIG. 3 shows a first embodiment of the wide band amplifier 1.

In the figure, 103 is a video signal source, T
1 is an input terminal, T2 is an output terminal, V3 is an operating power supply, V1
And V2 are bias power sources, 11 is a differential amplifier circuit, Q1 to Q10 are bipolar transistors, and I1 to
I4 is a constant current circuit, R1 to R3 are resistors, C1 is a capacitor, and R4 and R5 are termination resistors.

3.0 V is applied to the operating power supply V3.
About 1.9V is applied to the bias power source, and about 1.2V is applied to V2. The transistors Q1 to Q10 are
Q1, Q2, Q3, Q5, Q8, Q10 are npn type,
Q4, Q6, Q7 and Q9 are pnp type.

Here, Q1, V1 and C1 form a DC clamp circuit, V1 (1.9 V) is applied to the base of Q1 and C1 is charged to the emitter of Q1, thereby inputting at the input terminal T1. The minimum potential of the signal can be made equal to about 1.2 V, which is equivalent to subtracting the base-emitter voltage Vf (= about 0.7 V) of Q1 from V1.

To the in-phase input (+) of the differential amplifier circuit 11,
A video signal having a minimum potential of 1.2 V is input by Q1. In addition, the inverting input (-) has Q1
The same voltage (1.2 V) as the lowest potential is input by the emitter follower operation of Q2 to which the same base voltage is applied.

I3, I4, Q4, Q5, Q6, R3, V
Reference numeral 2 forms a voltage-current conversion circuit by a current mirror, which converts the output signal of the differential amplifier circuit 11 from voltage to current and transmits it.

Q7, Q8, Q9 and Q10 form a push-pull type output circuit, which is driven by the signal current mirror-transmitted to Q5 and Q6. Q7 and Q9 and Q8 and Q
10 are current mirrors, and the current ratio of the current mirrors is set to be Q7 << Q9 and Q8 << 10 depending on the emitter size ratio of the transistors.

Q2, I1, R1, R2 and I2 form a circuit for negative feedback, and apply negative feedback from the output terminal T2 to the input side of the differential amplifier circuit 11 and to a predetermined offset (I2 ×) to the feedback voltage. It is designed to have R2). That is, the potential negatively fed back from the output terminal T2 is (I2 × R) higher than the potential actually appearing at the output terminal T2.
2) It is designed to be biased low.

Next, the operation will be described.

The wideband amplifier 1 shown in FIG.
2, by negative feedback by R1, amplification operation is performed with a voltage gain of (R1 + R2) / R1. As a result, the input terminal T1
The video signal whose minimum potential (the tip potential of the synchronizing signal) is set to 1.2V is DC-amplified into a signal having a voltage amplitude level of (R1 + R2) / R1 and appears at the output terminal T2. Therefore, if R1 = R2 is selected, when a 1.0 Vpp video signal is applied to the input terminal T1,
A 2.0 Vpp video signal is output from the output terminal T2.

If I2 is set so that 0 <I2 × R2 <0.5V, the potential negatively fed back from the output terminal T2 is biased lower by 0.5V, so that the output terminal T2 is biased. The lowest potential that appears is set to a constant potential in the range of 0 to 0.5 V, and a 2.0 Vpp video signal is added to this lowest potential (0 to 0.5 V) and output.

As described above, the output potential of the amplifier 1 when there is no signal is set to 0.5 V or less with respect to the reference potential. Therefore, even if the output terminal T2 of the amplifier 1 is directly connected to the terminating resistors R4 and R5, the DC current that constantly flows from the output terminal T2 of the amplifier 1 to the terminating resistors R4 and R5 is suppressed to a small level, and space is saved. It eliminates the need for a large-capacity coupling capacitor that hinders

Further, when the 2.0 Vpp video signal is output, the change range of the output potential of the amplifier 1 is such that the minimum potential is 0.5 V or less and the maximum potential is 2.0 Vpp + 0.5 V =
It is 2.5V and can be reasonably kept within the output dynamic range obtained under a single power supply voltage of 3V. That is, even if the amplifier is operated under a low power supply voltage of 3V, the standard output signal of 2.0Vpp can be taken out without difficulty.

For example, in the amplifier 1 shown in FIG. 3, the amplitude of the output signal is Vomax, and R4 = R5 = 75.
Ω, Q7 and Q9 and Q8 and Q10 have emitter size ratios of 1:10 and R3 = 150Ω, respectively,
The signal amplitude V'max appearing at both ends of 3 is And the amplitude of the output signal is significantly smaller than 2.0 Vpp.

Therefore, the base-emitter voltage of Q7 is Vf7 and the collector-emitter saturation voltage of Q5 is Vs.
If at7 and V2 = 1.2V, then V3> Vf7 + Vsat5 + V'max / 2 + V2>
0.7 + 0.3 + 0.1 + 1.2 = 2.3V. That is, if the power supply voltage V3 is 2.3 V, Q5
Need not be saturated. Therefore, if the power supply voltage V3 is 3.0 V, the standard output signal of 2.0 Vpp can be taken out with a margin.

As a result, it is possible to reduce the power supply voltage of the wideband signal transmission circuit from 5V to 3V while ensuring the standard impedance matching condition and the standard amplitude level, thus saving power and space in AV equipment and the like. It will be possible.

FIG. 4 shows a second embodiment of the wide band amplifier 1.

The difference from the embodiment shown in FIG. 3 will be described. In the amplifier 1 shown in FIG. 4, the constant current circuit I2 of FIG. 3 is used as the circuit means for setting the minimum potential of the amplifier output to 0.5 V or less. Instead of the resistor R6 and the bias voltage source V
4 are provided. In this circuit, (V4-V1) /
As in the case of FIG. 3, the minimum potential (0.5 V or less) of the amplifier output can be precisely set by R6.

FIG. 5 shows a third embodiment of the wide band amplifier 1.

The amplifier 1 shown in the same figure is a modification of the amplifier shown in FIG. 3, in which a signal voltage which has been subjected to voltage-current conversion at Q3 to Q6 is flowed to R7 and R8, and R7 / R9 = R8 / R9 = n.
Current amplification is performed due to the relationship of> 1. In this circuit, it is possible to operate under a power supply voltage that is one step lower by reducing the vertically stacked voltage of the voltage-current conversion circuit, that is, by reducing the number of transistors connected in series to the power supply voltage V3. .

FIG. 6 shows the connection relationship of AV equipment having the wideband signal transmission circuit by the wideband amplifier 1 in the video signal output section, and the exchange of the video signal between the AV equipment is 75Ω / 1. It is performed by a standard signal unified to 0.0 Vpp.

The invention made by the present inventor has been specifically described above based on the embodiments, but the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the invention. Needless to say.

For example, wide band amplifier 1 may be partially or entirely formed of MOS transistors.

In the above description, the case of applying the invention made by the present inventor to the composite video signal transmission circuit which is the field of application which is the background of the invention has been mainly described, but the invention is not limited to this. It can also be applied to transmission of video signals decomposed into RGB.

[0060]

The effects of typical inventions disclosed in the present application will be briefly described as follows.

In other words, it is possible to reduce the power supply voltage of the wideband signal transmission circuit from 5V to 3V while ensuring the standard impedance matching condition and the standard amplitude level, which enables power saving and space saving in AV equipment and the like. The effect of turning on is obtained.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a wideband signal transmission circuit to which the technique of the present invention is applied.

FIG. 2 is a diagram showing an example of an output waveform of a wide band amplifier which constitutes a wide band transmission circuit according to the present invention.

FIG. 3 is a circuit diagram showing a first embodiment of a wideband amplifier according to the present invention.

FIG. 4 is a circuit diagram showing a second embodiment of a wideband amplifier according to the present invention.

FIG. 5 is a circuit diagram showing a third embodiment of the wideband amplifier according to the present invention.

FIG. 6 shows an A having a wideband signal transmission circuit according to the present invention.
Diagram showing the connection relationship of V equipment

FIG. 7 is a diagram showing a schematic configuration of a conventional wideband signal transmission circuit.

FIG. 8 is a diagram showing an output waveform example of a conventional wide band amplifier.

FIG. 9 is a diagram showing an output waveform in which direct current is cut by a coupling capacitor.

FIG. 10 is a diagram showing a schematic configuration of a wideband signal transmission circuit examined prior to the present invention.

[Explanation of symbols]

 100 AV equipment 101 Wideband signal transmission circuit 1 Wideband amplifier R4, R5 Termination resistor 103 Video signal source T1 input terminal T2 output terminal V3 Operating power supply (3.0V) V1 V2 Bias power supply 11 Differential amplifier circuit Q1 to Q10 Bipolar transistor I1 to I4 constant current circuit R1 to R9 resistor C1 capacitor

Claims (7)

[Claims] 1. A wideband signal transmission circuit for transmitting a signal by terminating the output of a wideband amplifier operating with a single power supply with a resistor, wherein the output potential of the amplifier when there is no signal is 0. A wideband signal transmission circuit comprising circuit means for setting the voltage to 5 V or less and directly connecting the output of the amplifier to the terminating resistor. 2. The wideband signal transmission circuit according to claim 1, further comprising circuit means for adjusting the minimum potential of the output signal input to the terminating resistor to a constant potential of 0.5 V or less. 3. A wide band amplifier which operates with a single power source and has a direct current amplification output, and circuit means for setting an output potential appearing at the output when no signal is input to 0.5 V or less with respect to a reference potential. Wide band amplifier characterized by having. 4. The wide band amplifier according to claim 3, further comprising circuit means for adjusting the minimum potential of the output signal to a constant potential of 0.5 V or less. 5. A DC clamp circuit for aligning the minimum potential of an input signal to a constant potential, and a signal whose minimum potential is aligned by this DC clamp circuit is DC amplified so that the minimum output potential is 0.5 V or less. The wideband amplifier according to claim 3 or 4, further comprising a wideband amplifier circuit for outputting. 6. A direct current amplified output of a video signal is directly connected to a terminating resistor, and a minimum potential of an output signal input to the terminating resistor is set to 0.5 V or less with respect to a reference potential. AV equipment characterized by having a video output circuit. 7. The AV according to claim 6, further comprising a video output circuit that outputs the sync signal included in the video signal by aligning the tip potential of the sync signal to a constant potential of 0.5 V or less.
machine.