JP2846034B2 - High frequency amplifier circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Applicability] The present invention relates to an amplifier using a complementary transistor circuit (particularly, a video amplifier for amplifying a video signal), and particularly to a CRT display device with high definition and low power consumption. An object of the present invention is to provide an element circuit suitable for electric power.

[Conventional technology]

High-definition CRT display devices, which are known as so-called computer CRT display devices, require high definition from the currently mainstream 1M pixel display to 2M and 4M pixels, and the video amplification system has been increased from 100MHz to 150MHz. It is becoming increasingly necessary to increase the bandwidth to 300 MHz. In addition, since the output requires a large amplitude of 40 to 50 Vpp and a DC bias level of 100 V, high precision and low power consumption are also required.

A video amplifier, which is one of the main objects of the present invention, is described in, for example, Japanese Patent Application Laid-Open No. 61-228778, "Amplification Circuit", and includes a monolithic stage including functions of a video multiplexer, a gain controller, a current amplifier and the like. It is disclosed as a driven high voltage cascode amplifier.

U.S. Pat.No. 4,494,075 eliminates distortion caused by changing the V _{BE of} the current mirror according to changes in signal current by using one of the current mirrors of opposite polarity on the load side of the multiplier as a Darlington circuit. Is described.
US Pat. No. 4,293,875 describes a video amplifier of a type in which a cathode of a CRT is driven by a complementary transistor push-pull circuit using a bias circuit with a level shift. Further, US Pat. No. 4,051,521 describes a composite signal video amplifier which drives a high voltage cascode amplifier with a low voltage complementary emitter follower amplifier.

Furthermore, "new low frequency high frequency circuit design manual" CQ
(Published by 1988, April 30, first edition), p258 to 259, describe the use of a complementary transistor circuit as a differential analog switch.

Also, relatively recent research results on wideband video amplification systems for high-definition CRT display devices have been reported in 1989 as a model that provides high-precision high-frequency output stage feedback. Circuit Conference Digest of Technical
Papers, pp. 70-71 (1989 IEEE International S
olid-State Circuits Conference Digest of Technical
Papers pp. 70-71 (Feb. 1989)). Further, for the cascode type in which no high-frequency feedback is performed from the high-frequency output stage, see IEE Transaction on Consumer Electronics, Vol. 34, No. 3, August 1989, pp. 426-433 (IE
EE Transactionson Consumer Electronics, Vol. 34, No.
3, AUGUST 1988 pp.426-433).

[Problems to be solved by the invention]

Here, the prior art described in the above-mentioned Japanese Patent Application Laid-Open No. 61-228778 can satisfy the necessity in terms of functions, but sufficient consideration has not been given to simplification of each functional circuit and reduction of the number of amplification stages. There has been a problem that the circuit configuration is complicated and it is difficult to respond to the increase in the operating frequency band. Also, USP3 mentioned earlier
Documents such as the subject and differential analog switch describe elementary technologies such as complementary transistor circuits individually, but as in the present invention, the complementary transistor circuit is used as a gain controller for a video amplifier and a current mirror circuit for an output stage. Nothing is mentioned about the simplification by using it all over.

Further, among the above prior arts, the high frequency negative feedback system has a gain margin at a high frequency due to a delay of a circuit loop,
Instable phenomena such as oscillation become apparent due to insufficient phase margin, and the negative feedback loop from the high-voltage output stage itself becomes a load on the amplifier and consumes high-frequency power, thus limiting the broadband operation. I have.

In the cascode amplification method of the above-described conventional techniques, it is possible to omit the high-frequency signal negative feedback path from the output stage by accurately maintaining the signal current of the cascode stage. Since the problem can be avoided, a wider band can be achieved. However, even in the cascode system, a negative feedback path for DC regeneration for generating a reference DC voltage corresponding to the back porch point of the video signal to the amplifier output voltage cannot be omitted, so the feedback path still connected to the high voltage output stage Remains as a load, which is a limiting factor in widening the bandwidth and reducing power consumption. The reason is that the high-precision feedback resistor connected to the high-voltage output stage is large in size to withstand relatively large power consumption and large in power consumption (∝ΔCV ² f) due to its parasitic capacitance. In addition, the parasitic load (for example, 1 to 2 PF) tends to be reduced year by year due to technological progress of the cathode load capacity (for example, 4 to 6 PF) of a high-definition CRT, and the ratio is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a high frequency amplifier circuit having a wide band and low power consumption.

[Means for solving the problem]

The above object has a first high-voltage output transistor connected to a load, and a plurality of second low-voltage transistors cascode-connected to the first high-voltage output transistor,
By inputting an input signal to a plurality of second transistors, a high-frequency amplifier driving a first high-voltage output transistor is biased in common with the plurality of second transistors to form a current mirror with the plurality of second transistors. Can be achieved by using the current flowing in the third transistor constituting the above as a feedback signal to the input signal for DC component reproduction.

[Action]

According to the present invention, a third transistor having a similar relationship to the first high-voltage output transistor is provided, and a signal equivalent to the output of the first high-voltage output transistor is indirectly output to the third transistor.
The direct feedback from the high-voltage output stage is omitted altogether by reducing the load on the high-voltage output stage, thereby reducing the load on the high-voltage output stage. Power consumption can be reduced.

〔Example〕

 Hereinafter, one embodiment of the present invention will be described with reference to FIG.

FIG. 1 is a circuit block diagram of an indirect feedback type video amplifier of the present invention and a CRT display device using the same.

The video amplifier in FIG. 1 includes a low-voltage driving stage 80 composed of an LSI circuit and an output stage 70 of a high-voltage amplifier, and the driving stage 80 and the high-voltage output stage 70 constitute a cascode amplifier. It is connected.

From the signal source E _S is the input of the driving stage 80 of the low voltage 75Ω termination resistor R _S, the analog video signal is applied via a coupling Kiyapashita C _X1 of large capacity. The output of the high voltage output stage 70 is connected to the cathode electrode of the CRT via a bias voltage source 75 for brightness control, and the video signal applied to the input terminal T11 of the drive stage 80 is amplified and the cathode electrode of the CRT is amplified. Drive and display CRT according to applied signal.

Configuration of the driving stage 80, two inputs of Buffered multiplexer input stage, voltage / current (V / I) converter circuit 20 having a conversion impedance Z _X, which is connected to its output side, and further,
Next, a gain controller 31 using a multiplication function is connected. The gain controller 31 is _supplied with a control voltage from a resistor _RG2 via a control circuit 32 and a resistor _RG1 .

The output of the gain controller 31 has two current outputs having phases opposite to each other.
Output stage current mirror amplifier
Connected to drive 51-54.

The feedback current mirror amplifier 69 is connected via an external resistor R _F
The output is connected to a 5 V power supply V _CC , and its output is connected to the input via the sampling switch 61, the capacitor C _X2 , the amplifier 62, and the resistors R ₈₉ and R ₉₀ so as to be negatively fed back to the input.

The outputs of the output stage current mirror amplifiers 51 to 54 are collectively connected to the high voltage output stage 70. High voltage output stage 70
Is high voltage power transistor 71, diode 72, load resistance
It is composed of a circuit composed of _RL and a buffer amplifier composed of transistors 73 and 74.

The video amplifier configured as described above has a gain of 10
This is an inverting amplifier with a high voltage output of about 0 times. Here, the input voltage to the drive stage 80 is v _i , the output voltage of the output stage 70 is v ₀ , the internal gain of the drive stage 80 is K, the external impedance of the V / I converter is Z _X , and the high voltage output Assuming that the load resistance of the stage 70 is R _L , the output voltage v ₀ is as shown in equation (1).

Here, K is a value that changes according to the control voltage of the gain controller 31.

As shown in FIGS. 2 (a) and 2 (b), the video input signal is provided as an AC signal having a maximum of about 1 V _PP , while the output signal for controlling the cathode of the CRT is a superimposed predetermined DC high voltage. Therefore, it is necessary to reproduce a stable and accurate DC component. This reference DC level is performed at the time shown as the back porch after the horizontal synchronization pulse in the waveforms of FIGS. 2 (a) and 2 (b). The operation of the embodiment of the present invention shown in FIG. 1 is performed as follows.

When a periodic sampling pulse at the time of the back porch is applied to the sampling control terminal T61 of the sample and hold switch 61 in FIG. 1, the feedback voltage from the feedback current mirror circuit 69 passes through the sampling switch 61 to the capacitor C _{X2 of the} hold circuit. Charge, amplifier 62, bias resistor
It is fed back to the input via the R _89. The DC loop gain of this feedback loop is several hundred times. This feedback is a constant value amplifier after sufficient time longer than the time constant of C _X1 · R ₉₀ in the input stage because it is a negative feedback for feeding back the voltage drop due to external resistance R _F of the positive phase of the current mirror 69 Calm down. Here, the reference DC level at the time of the back porch will be considered.
The current flowing through the output stage current mirror amplifiers 51 to 54 is represented by I ₀ ,
Assuming that the current flowing through the feedback current mirror amplifier 69 is I ₀ / N, the DC output voltage of the high voltage output stage 70 is V ₀ , the feedback voltage from the feedback current mirror amplifier 69 is V _F , and the high voltage output stage The power supply voltage of 70 is V _H and the power supply voltage of the low-voltage drive stage 80 is V
Output voltage V ₀ which DC component to the _CC, a feedback voltage V _F is the formula (2)
Can be expressed as

When I ₀ is deleted from the equation (2), it can be expressed as follows.

That (V _B -V ₀₎ of formula (3) is intended for determining the output amplitude, which indicates that the determined by _{NR L / R F · (V} CC -V F), a desired output amplitude In order to obtain V _F , change V _F by the reference terminal T63 of the amplifier 62 or R _F
Can be changed.

The feedback in the video amplifier shown in FIG. 1 is an indirect feedback performed by generating a feedback current similar to the output current. However, the ratio N when using a current mirror circuit depends on the emitter size ratio of the transistor. large current I ₀ for that, it is possible to control the stable for highly accurate output voltage irrespective of the small range.

Thus, no feedback impedance element is required in the high-voltage output stage 70, power consumption (ΔCV ² f) due to the parasitic capacitance is eliminated, and wideband operation with low power consumption becomes possible. Also, since the feedback has a low voltage amplitude, the response of the feedback is fast. Further, it is also useful in terms of miniaturization and reliability.

FIG. 3 shows another embodiment of the indirect feedback video amplifier.
In the figure, the video amplifier comprises a low-voltage drive stage 80, a high-voltage output stage 70, a sample-and-hold circuit 60, etc., and the input terminal T11 of the low-voltage drive stage 80 is connected via an input capacitor C _X1. An input signal (not shown) is applied to terminal 1. The output of the high voltage output stage 70 is connected to the cathode R of the CRT. 3 are a high voltage power supply + V _H (for example, 120 V) and a low voltage power supply + V _CC (for example, 10 V).

The high-voltage output stage 70 includes a load resistance _RL of several hundred ohms and a high-frequency power transistor 71, and has a base _{supplied with} a fixed voltage of + V _CC . The emitter of the power transistor 71. The output stage current mirror 51, 52 and 53 of the low pressure section is connected to the emitter resistor R _E1, constitute a so-called cascode amplifier. Output stage current mirrors 51 and 5
Transistor Q69 and emitter resistor R _E2 in which the base common 2, 53 are connected in parallel, their common base connected to the output of the preamplifier 81. The collector of the transistor Q69 is connected through a resistor R _F in the power supply + V _CC,
The signal is input to the switch 61 of the sample and hold circuit 60. The output side of the switch 61 is the hold capacitor C _X2 and the amplifier 6
2 is connected to the input side. The other input of the amplifier 62 receives a divided voltage of the power supply + V _CC composed of the resistors R601 and R602,
The output 63 of the amplifier 62 is connected via a resistor R89 to the input of a preamplifier 81. The loop gain of this closed loop is
It is about 0.

In FIG. 3, the reference DC level at the time of the back porch will be considered. The output voltage of the DC component of the high voltage output stage 70 is V ₀ , and the feedback voltage from the corresponding transistor Q69 is
Assuming that V _F , the emitter-base voltage of the transistors Q69, 51, 52, 53 is V _BE , and the output voltage of the amplifier 81 is V _A , the output voltage V ₀ and the feedback voltage V _F of the direct current are expressed by the following equations (5). , (6).

If V _A −V _BE in equations (5) and (6) is eliminated, it can be expressed as equation (7).

However, (V _H −V ₀ ) in the equation (7) indicates the output amplitude. Thus, the variable resistor R _F in FIG. 3 so as to satisfy the desired for V ₀ (7) equation is set.

With the above configuration, when a sampling pulse is applied to the control input terminal T61 of the sample and hold circuit 60 during the period shown as the back porch of the waveform of FIG. 2, it corresponds to the output voltage during the back porch. The sampled and held voltage is sampled and held, compared with a reference value, and negatively fed back to correct the output voltage via the amplifier 62 and the resistor R89. Since the sampling pulse is periodically applied every horizontal synchronization (1H period), the DC voltage of the output voltage finally becomes equal to the desired value which has been set, and holds the value. It should be noted that in the above-described equation (7) and the configuration of FIG. 3, the relationship between the output voltage and the feedback voltage is a symmetric differential relationship independent of temperature and the like. Therefore, control is performed with the same good accuracy as feedback from the high voltage output stage.

As a result, the output and voltage bias can be controlled only by the circuits of the low-voltage drive stage. As a result, the load on the high-voltage output stage is reduced (about 1 to 2 PF), and the bandwidth is improved by several tens of percent. In addition, it is possible to reduce high-frequency power consumption. Further, it is desirable to omit the feedback resistor in the high voltage output stage from the viewpoint of cost and reliability, and it is easy to integrate circuits.

FIG. 4 shows an embodiment of an indirect feedback video amplifier applied to the embodiment of FIG.

FIG. 5 shows another embodiment of the indirect feedback video amplifier, which is different from the embodiment of FIG. 4 in that a peak hold circuit 65 is used instead of the sample and hold circuit 60 of FIG. This peak hold circuit 65 includes diodes 66 and 6
7, consisting of resistors R601 to R603, capacitor _CX , amplifier 62,
The peak value of the voltage generated by the diode 66 and the capacitor C _X to the terminal T85 (voltage polarity generated at the terminal T85 is same as is the polarity of the output) is to hold. Thereby, a voltage corresponding to the back porch level of the video signal can be obtained without using a timing signal as in FIG. 4, and the same effect as in FIG. 4 can be obtained. Note that diode 6
7. The circuit composed of the resistor R603 is for adjusting the input operating point of the amplifier 62.

〔The invention's effect〕

(1) According to the present invention, the equivalent load on the amplifier output side can be reduced, and since most circuits operate in the DC mode, high-speed, wide-band operation is possible. Specifically, the bandwidth of the video amplifier is 250MHz to 300MHz and high definition CRT with 5M pixels or more
Display device can be realized, 500M band only with IC driver
Hz is realized.

(2) According to the present invention, since operation can be performed with a current signal, the dynamic range of the signal can be widened and high accuracy can be achieved. According to the present invention, an accuracy of ± 0.5% or less can be easily achieved in a required signal range.

(3) For the above-mentioned reason, it is possible to operate with a low voltage power supply, to reduce power consumption, and to facilitate integration.

(4) According to the present invention, since the circuit scale is small and simple, the cost can be reduced and the reliability can be improved.

(5) According to the present invention, since differential operation is performed with a current signal and as necessary, S /
N ratio can be improved.

(6) For the same reason, it is easy to shift the level of addition and subtraction of a signal, and it is easy to cope with a new function.

(7) By dividing the output stage according to the present invention, the effective lead inductance of the terminal can be reduced, and the band of the high voltage output stage can be easily widened.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing an embodiment of the present invention, and FIG.
FIG. 3 is a diagram showing input / output waveforms of a video signal, FIG. 3 is a circuit diagram showing another embodiment of the indirect feedback video amplifier, and FIG. 4 is a circuit of the indirect feedback video amplifier shown in the embodiment of FIG. FIG. 5 shows another embodiment of the indirect feedback video amplifier. FIG. 20: V / I conversion circuit, 31: gain controller, 40:
... Auxiliary current mirror amplifier, 51-54 ... Output stage current mirror amplifier, 61 ... Sample hold switch, 62
……Amplifier

 ──────────────────────────────────────────────────続 き Continuation of the front page (31) Priority claim number Japanese Patent Application No. 1-118665 (32) Priority date Hei 1 (1989) May 15 (33) Priority claim country Japan (JP) (72) Inventor Takashi Sase 4026 Kuji-cho, Hitachi City, Ibaraki Pref.Hitachi, Ltd.Hitachi Research Laboratory Co., Ltd. (72) Inventor Kenkichi Yamashita 5-2-1 Omika-cho, Hitachi City, Ibaraki Pref. 60-51309 (JP, A) JP-A-61-274410 (JP, A)

Claims (1)

(57) [Claims] 1. A signal according to an input signal, comprising: a first high-voltage output transistor connected to a load; and a plurality of second low-voltage transistors cascode-connected to the first high-voltage output transistor. Is input to the plurality of second transistors to drive the first high-voltage output transistor. In the high-frequency amplifier, the bias is commonly biased to the plurality of second transistors and the plurality of second transistors are A high-frequency amplifier circuit, wherein a current flowing through a third transistor connected to a low-voltage source constituting a current mirror is used as a negative feedback signal to said input signal for DC component reproduction.