JP2001053980A - Driver circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a driver circuit for driving a driver amplifier at low power voltage of 3V system. SOLUTION: A driver amplifier 100 is an amplifier of a current outputting type in which a buffer circuit 10, which amplifies the voltage of an input signal vi by a gain 1 to obtain a current im according to the voltage, is provided as an inputting stage and a current amplifier circuit 12, which amplifies the current im by an amplification factor (m) to output, is provided as an outputting stage. A feedback resistor R2 for negatively feeding back current is connected between its output terminal 18 and a second terminal 16 on the output side of the circuit 10, and an output resistance is set to be the same value as a load RL by setting the resistance R2 and the current amplification factor (m) to be prescribed values. Thus, serial resistance to be matched with a load is removed to directly supply output from the amplifier 100 to the load, thereby its dynamic range can nearly be halved and a power voltage can be dropped.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a driver circuit for obtaining a predetermined signal output, and more particularly to a driver circuit suitable for use in a signal output circuit of a video device such as an electronic still camera or a video camera.

[0002]

2. Description of the Related Art As is well known, in an apparatus for handling a video signal, an input / output circuit of the video signal is, for example, 75 input / output circuits.
It is configured to be exchanged as a video signal that is matched by Ω impedance and has little reflection or distortion. In this case, at the video input side where the signal amplitude is standardized, a load resistance of 75
It is necessary to obtain a video signal of about 1.2 V _pp .

Conventionally, as a driver circuit for a device on the video output side as described above, for example, as shown in FIG.
It is known that a driver amplifier such as an operational amplifier is connected in series with a resistor of 75Ω and a coupling capacitor to produce a line-out output. As an operational amplifier applied to a driver amplifier, one having an input stage such as a differential amplifier circuit and an output stage such as a push-pull emitter follower circuit is known. That is, an amplifier that obtains high-precision output with high input impedance and low output impedance has been applied.

[0004] The driver amplifier is driven at a predetermined power supply voltage V _cc, such as from a battery, such as non-in-inverting terminal input signal is supplied, and a predetermined bias voltage to the inverting terminal is supplied. The differential voltage of the input signal is amplified by a predetermined gain in a differential amplification stage, and is amplified to a predetermined signal amplitude through an output stage and output. The output signal from the driver amplifier is removed of the DC component by a coupling capacitor, and further supplied from a line-out output through a 75Ω series resistor to a 75Ω load on the video input side via a predetermined cable. In this case, the output voltage of the driver amplifier is divided into a 75Ω series resistor and a 75Ω load on the video input side. Therefore, the load on the video input side must be at least
In order to obtain a signal amplitude of 1.2 V _pp , the output gain of the driver amplifier was set so as to obtain a signal amplitude of 2.4 V _pp .

[0005]

By the way, an electronic still camera or a video camera integrated VTR (Video Tape Recorder)
In portable video equipment such as a rder), power saving has been achieved for battery driving, and for example, those driven by a 3V system power supply voltage have been developed.

However, as described above, in the prior art, the driver amplifier is composed of an operational amplifier having a low output impedance and outputs the output through a 75Ω series resistor, so that 1.2 V _{pp is} applied to the 75Ω load on the video input side. In order to supply the video signal, a driver amplifier output required a signal output of 2.4 V _pp . In order to obtain the signal output by the driver amplifier having the above configuration, for example, when a bipolar transistor is used in the push-pull circuit of the output stage, a driving voltage of about 2 V is required for the transistor. The power supply voltage _Vcc is at least (2V + 2.
4V) The power supply voltage had to be higher than that, that is, 5V power supply voltage. By the way, the driver amplifier is CMOS (Comp
Complementary Metal Oxide Semiconductor) also has a similar problem when it is configured with a transistor. This makes it impossible to use the power of 3V system as _the power supply voltage V _cc which drives the driver amplifier to the power supply, it is necessary to provide a 5V power supply only for the driver circuit, miniaturization and power saving of the power supply circuit Was hampered in planning.

An object of the present invention is to solve the above-mentioned problems and to provide a driver circuit which can be driven by a low power supply voltage of 3V system, and therefore can save power and reduce the size of the power supply circuit. And

[0008]

According to the present invention, there is provided a driver circuit for amplifying an input signal to a desired signal amplitude and supplying the amplified signal to a load. A buffer means for obtaining a current; a current amplifying means for amplifying and outputting a current flowing through an output terminal of the buffer means at a predetermined amplification factor; and a predetermined feedback resistor from the output terminal of the current amplifying means to the output terminal of the buffer means. Including feedback means for performing negative feedback through, setting the signal gain and output resistance of the entire circuit to desired values based on the current amplification factor of the current amplification means and the resistance value of the feedback means,
An output signal amplified to a predetermined level from an output terminal of the current amplifying means is supplied to a load.

In this case, as the buffer means, a voltage follower circuit which amplifies the voltage applied to the first terminal with a gain of "1" and outputs the amplified voltage to the second terminal is advantageously applied, and the output of the voltage follower circuit is preferably used. Preferably, the current amplifying means is mirror-connected so as to detect the current, and a feedback resistor of the feedback means is connected between the output terminal of the current amplifying means and the second terminal of the buffer means.

In this case, an input signal is supplied to a first terminal of the buffer means, a predetermined bias is applied to a second terminal, and the input signal from the first terminal is non-inverted and amplified to load a load. Is preferably formed.

Further, an inverting amplifier in which a predetermined reference voltage is applied to a first terminal of the buffer means, an input signal is supplied to a second terminal, and the input signal is inverted and supplied to a load. .

On the other hand, a driver circuit according to the present invention is a driver circuit for amplifying an input signal to a predetermined signal amplitude and supplying the amplified signal to a load, wherein the voltage-current conversion means converts a voltage corresponding to the input signal into a current, A voltage-current converter for converting a differential voltage between the non-inverting terminal and the inverting terminal into a current with a predetermined conversion coefficient, and amplifying and outputting the current obtained by the voltage-current converter with a predetermined amplification factor Current amplification means, and feedback means for performing negative feedback from an output terminal of the current amplification means to an inversion terminal of the voltage-current conversion means via a predetermined feedback resistor;
The signal gain and output resistance of the entire circuit are set to desired values based on the conversion coefficient of the voltage-current converter, the amplification factor of the current amplifier, and the resistance of the feedback unit, and a predetermined value is output from the output terminal of the current amplifier. Is supplied to the load.

In this case, the voltage-current conversion means includes a first buffer for obtaining a voltage corresponding to the voltage applied from the non-inverting terminal, a second buffer for obtaining a voltage corresponding to the voltage applied from the inverting terminal, A conversion resistor for connecting the output of the buffer to obtain a current corresponding to the differential voltage, wherein the current amplification means is mirror-connected so as to detect a current flowing to one buffer output of the voltage-current conversion means, and It is preferable to form a differential amplifier in which the feedback resistor of the feedback means is connected between the output of the amplification means and the inverting terminal of the second buffer.

Further, in this case, an input signal is supplied to the non-inverting terminal of the voltage-current converting means, and a predetermined bias is applied to the inverting terminal. It is preferable that the non-inverting amplifier be supplied.

Also, a predetermined reference voltage is applied to the non-inverting terminal of the voltage-current converting means, an input signal is supplied to the inverting terminal, and the input signal from the inverting terminal is inverted and amplified and supplied to the load. It may be.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of a driver circuit according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
1 shows an embodiment of a driver circuit according to the present invention. The driver circuit according to the present embodiment is, for example, a video output circuit applied to a portable video device such as an electronic still camera. The driver circuit is, for example, a line driver connected to a TV monitor or the like via a cable 500 having a characteristic impedance of 75Ω and supplying a video signal having a signal amplitude of at least about 1.2 V _pp to a 75Ω load RL of the video input circuit. .

In particular, the driver circuit of the present embodiment is configured such that a negative feedback resistor R2 and a resistor R1 are externally connected to a current output type driver amplifier 100 including a buffer stage 10 and a current amplification stage 12, and the current amplification stage 12 By setting the output gain and the output resistance to desired values based on the current amplification factor m and the values of the feedback resistors R2 and R1, for example, by setting the output resistance to 75Ω, the cable 500 is directly driven without passing through a 75Ω series resistance. Is the main feature.

More specifically, in the driver circuit according to the present embodiment, as shown in FIG. 1, a bias circuit 200, a feedback circuit 300, and a coupling capacitor 400 are connected to a driver amplifier 100 so that a desired video signal can be obtained. Is formed. Driver amplifier 100 includes a buffer circuit 10 as an input stage, a two-stage configuration of amplifiers and a current amplifier circuit 12 as an output stage, a video signal v _i is supplied to the buffer circuit 10, the output current i _This is a current output type amplifier that detects _m , amplifies it at a predetermined amplification factor m in the current amplification circuit 12, and outputs the amplified signal.

The buffer circuit 10 at the input stage amplifies an input signal with a gain of "1". For example, a voltage follower circuit is advantageously applied to the buffer circuit 10, and its output side has a voltage _Vm and a current corresponding to the input signal. an amplification circuit for outputting the i _m. In this embodiment, the first terminal 14 a video signal v _i is supplied is provided on the input side, a second terminal 16 of the bias circuit 200 and the feedback circuit 300 is connected is provided on the output side. The bias circuit 200 includes a bias resistor R1 and the voltage source V _R, a circuit for biasing the buffer circuit 10 to a predetermined DC voltage.

On the other hand, in the driver amplifier 100, the current amplifier circuit 12 at the output stage thereof
Mirrored to detect the output current i _m of connection, a current mirror circuit for amplifying the output current i _m with a predetermined amplification factor m is advantageously applied, the output of driver amplifier 10
It is formed as a zero output terminal 18. The output terminal 18, the current amplified output current _(m · i m) is output.

The feedback circuit 300 outputs the output of the current amplifier circuit 12,
That is, the current amplifier circuit is connected between the output terminal 18 of the driver amplifier 100 and the second terminal 16 of the buffer circuit 10.
A current feedback circuit for negatively feeding back the buffer circuit 10 a predetermined feedback current i _f of the output current _(m · i m) from 12. In the present embodiment, the feedback resistor is formed by a feedback resistor R2 and a resistor R1 having a predetermined value, and the feedback amount is determined by the value.
It sets the overall gain and output resistance of the entire driver circuit together with the amplification factor m of the current amplifier circuit 12.

On the other hand, the coupling capacitor 400 is an element that is connected in series to the output terminal 18 of the driver amplifier 100, removes a DC component from the output signal, and outputs a video signal having a predetermined signal amplitude from the output terminal _Vout. is there.

In such a configuration, the driver amplifier
When the video signal v _i is supplied to the first terminal 14 of the 100, the buffer circuit 10 is amplified by a gain "1" to the video signal v _i.
Thus, the voltage v _m corresponding to the input signal v _i to its output
And current i _m is output. That is, the voltage v _m of the second terminal 16 is represented by the following formula (1).

[0024]

[Number 1] _{v m = v i ··· (1} ) On the other hand, the current i _m of the output side of the buffer circuit 10 is amplified by the current amplifying circuit 12 with a predetermined amplification factor m, its output terminal
18 is output as an output current _(m · i m) from. At this time, the current from the output terminal 18 is negatively fed back to the second terminal 16 as the feedback current _if via the feedback resistor R2 of the feedback circuit 300.
Therefore, assuming that the current flowing to the coupling capacitor 400 side is i _o , the following equation (2) holds.

[0025]

[Number 2] _{m · i m = i o +} i f ··· (2) Further, the feedback current i _f, when the voltage of the output terminal 18 and v _o,
Voltage v _m of second terminal 16 of buffer circuit 10 and feedback resistance
The following equation (3) is obtained from the value of R2.

[0026]

Equation 3] _{i f = (v o v m} ) / R2 ··· (3) In addition, the feedback current i _f together with the current i _m from the second terminal 16, a bias which is connected to the second terminal 16 flows through the resistor R1, the following equation (4) holds the relationship between the resistance value R1 and the voltage v _m of the second terminal 16.

[0027]

[Expression 4] i _m + i _f = v _m / R1 (4) Therefore, the output signal v _o is determined by the resistance from the above equations (1) to (4).
Using R1 and R2 and the current amplification factor m, it can be expressed as shown in the following equation (5).

[0028]

Equation 5] _{v o = {1+ (R2 /} R1) · (m / (1 + m))} · v i - {R2 / (1 + m)} · i o ··· (5) the above equation (5) is For example, if the gain as shown in FIG.
An expression representing a driver circuit with an output resistance of R _o : v _o = A v _i −R _o i _o
Following equation total gain A and an output resistor R _o of the driver circuit according to this embodiment by comparing the preparative (6) can be obtained respectively at (7).

[0029]

A = 1 + (R2 / R1) · (m / (1 + m)) (6) _Ro = R2 / (1 + m) (7) For example, assuming that the output resistance _Ro is 75Ω. And the total gain A is almost doubled, and the values of the feedback resistor R2, the bias resistor R1, and the current amplification factor m are determined so as to satisfy the above equations (6) and (7). Can be set, for example, as follows. Current amplification factor m = 9, bias resistance R1 = 680, feedback resistance R2 = 750 When this driver circuit supplies an output signal to the termination resistance R _L = 75Ω, R _L = R _o = 75Ω, that is, i _o = v _o From / R _L = v _o / R _o , the above equation (5) becomes as shown in the following equation (8).

[0030]

Equation 7] _{v o = A · v i /} 2 ··· (8) Therefore, the conditions set as described above, the input signal v _i for example, when a 1.2V _pp, without using a 75Ω series resistor Then, the output signal _vo can be set to 1.2 _Vpp , and the output signal _vo can be supplied to the load _RL . That is, since an output resistance of 75Ω can be realized equivalently, 1.2V _PP can be supplied to the load resistance of 75Ω without generating 2.4V _PP .

As described above, according to the driver circuit of the present embodiment, the driver amplifier 100 having the buffer stage 10 and the current amplification stage 12 supplies the output current of the current amplification stage 12 to the buffer stage.
Feedback circuit connected to the second terminal 16 on the output side of 10
Is provided with the 300, that its feedback resistor R2 and the resistor R1, and sets the amplification factor m of the current amplification circuit 12 to a predetermined value, the output resistance R _o and overall gain A of the circuit to a desired value Can be. Therefore, the output resistance R _o as the same 75Ω terminating resistor R _L of the load, without connecting the 75Ω series resistor to the output of the driver amplifier 100, the output signal amplified to a desired value
As values of V _o, for example it can be supplied by the signal amplitude of 1.2V _pp.

[0032] In this case, the output dynamic range of the driver amplifier 100, the product of the total gain A and the input signal v _i 2
It is sufficient to obtain a signal amplitude of 1.2 V _pp without obtaining the same value, that is, an output of 2.4 V _pp .
Therefore, the power supply voltage of driver amplifier 100 can be made lower.

Next, FIG. 2 shows an embodiment of a driver circuit which further embodies the above embodiment. In the driver circuit according to the present embodiment, the driver amplifier 100 is configured by a bipolar transistor. Note that the same parts as those in the above embodiment are denoted by the same reference numerals and will be described.

More specifically, the driver amplifier 100 of the present embodiment
Are the first to fourth transistors as shown in FIG.
It includes a buffer circuit 10 formed by Q102 to Q108, and a current amplifier circuit 12 formed by fifth to eighth transistors Q110 to Q116. The buffer circuit 10 includes a front-stage transistor Q102, Q104 and a rear-stage transistor Q106, Q108, and forms a two-stage push-pull voltage follower circuit that amplifies an input signal with a gain of "1". .

On the other hand, the current amplifying circuit 12 is connected to the output transistors of the buffer circuit 10 by the transistors Q110 and Q112 in the preceding stage.
The current mirror circuit is connected to the collectors of Q106 and Q108, and the output current is mirror-connected by transistors Q114 and Q116 at the subsequent stage to amplify the current.

Seventh and eighth transistors Q11 at the subsequent stage
4, Q116 is formed of a multi-emitter transistor, and the current mirror ratio, that is, the current amplification factor can be set by the ratio of the emitter area of the transistors Q110, Q114 and Q112, Q116. Therefore, when formed in an IC, this current amplification factor can be set with very high accuracy.

The driver circuit of this embodiment, when applying the configuration of the driver amplifier 100 as described above, a video signal v _i is supplied via the first terminal 14 of the buffer circuit 10, the second The feedback resistor R2 and the resistor R1 between the output terminal 18 and the terminal 16 are connected to the terminal 16, and the bias circuit formed by the capacitor C is connected.

[0038] In this embodiment, the output gain A substantially 4, and an output resistor R _o and 75 ohms. When the respective values are obtained so as to satisfy the above equations (6) and (7), for example, the current amplification factor m = 9, the bias resistance R1 = 220, and the feedback resistance R2 = 750. As a result, a video signal having a signal amplitude of 0.6 V _pp is input and the output signal _vo is output with a signal amplitude of 1.2 V _pp to a terminating resistor of 75Ω.
Can be output as In this case, the power supply voltage _Vcc
A 3.3V power supply can be used as the power supply.

In order to clarify the effect of each of the above embodiments, for example, the conventional driver circuit shown in FIG. 9 and FIG. 10 or FIG.
The driver circuit shown in FIG. 9 has a driver amplifier (Amp)
An operational amplifier having a high input and low output impedance is used. Therefore, a 75Ω resistor is connected in series to the output to match with the load side _RL . In this case, the output of the driver amplifier Amp, when the signal amplitude to the load and 1.2V _pp, the signal amplitude of twice the 2.4V _pp is required. By the way, in the conventional example shown in FIG.
A negative voltage is applied to (−) to double the gain, for example, to obtain a signal amplitude of 2.4 V _pp . In each of the above embodiments according to the present invention, without using a series resistance of 75 ohms, the 75 ohms output resistor R _o of the circuit, since taking matching with the load, the signal amplitude 1.2V _pp as its output the above-described Can be output as is.

FIG. 10 shows an example in which the output stage of the driver amplifier Amp in the conventional driver circuit shown in FIG. 9 is constituted by a bipolar transistor. The operational amplifier has, for example, a differential amplifier circuit as an input stage and a push-pull voltage follower circuit as shown in FIG. 10 as an output stage. In this case, the emitter of the preceding minimum (min) voltage V _s and the rear stage of the transistor serving as a current source - the sum of the voltage V _be between the base (V _s + V _be) is required by at least 1V. Therefore, to obtain an output signal of 2.4 V _pp as described above, a power supply voltage of (2 + 2.4) V, that is, 5 V was required. In the above embodiment according to the present invention, it is possible to directly outputs the output signal v _o of 1.2V _pp, it can be the power supply voltage V _cc to 3.3V.

FIG. 11 shows an example in which the output stage of the driver amplifier Amp in the conventional driver circuit shown in FIG. 9 is constituted by MOS transistors. in this case,
When outputting a relatively large current, such as a 75Ω driver for video, it is difficult to reduce the source-drain voltage V _sd , and with a 3V power supply, it was limited to output about 2.0 V _pp . Therefore, at least a 5V power supply was required.

Next, FIGS. 3 and 4 show modifications of the driver circuits according to the above embodiments. This embodiment is different from the above embodiments in that the driver amplifier
Connect the DC source V _R to a first terminal 14 of the 100, and supplies the input signal v _i obtained by inverting through a resistor R1 to the second terminal 16,
The point is that an inverting amplifier for obtaining an inverted output signal v _o is formed. The same parts as those in the above embodiments are denoted by the same reference numerals and will be described.

[0043] That is, in this embodiment, the DC voltage V _R is applied to the first terminal 14, a video signal v _i is supplied via the second terminal 16, the video to the output side of the buffer circuit 10 current i _m flowing in response to the signal v _i. The current im is multiplied by _m in the current amplification circuit 12 and output from the output terminal 18.
At this time, if the feedback current is i _f , the current supplied to the load is i _o , and the voltage of the output terminal 18 at that time is v _o , the following equations (9), (10),
(11) holds respectively.

[0044]

[Number 8 _{m · i m = i o +} i f ··· (9) i f = v o / R2 ··· (10) i m + i f = v i / R1 ··· (11) these equations From (9), (10), and (11), the output voltage _vo at the output terminal 18 is expressed by the following equation (12).

[0045]

[Equation 9] _{v o = - (R2 / R1} ) · (m / (1 + m)) · v i - (R2 / (1 + m)) · i o ··· (12) Therefore, from the above equation (12) a total gain a of the circuit, the output resistor R _o is the following equations (13), it is expressed by (14).

[0046]

Equation 10] A = - (R2 / R1) · (m / (1 + m)) ··· (13) R o = R2 / (1 + m) ··· (14) Thus, 75 ohms output resistor R _o And the total gain is almost doubled, and from the above equations (13) and (14),
When the values of the input resistance R1 and the feedback resistance R2 are obtained,
For example, it can be set as follows. Current amplification factor m = 9, input resistor R1 = 330, feedback resistor R2 = 750 Consequently, the conditions set as described above, when the input signal v _i obtained by inverting e.g. -1.2 V _pp, the 75Ω series resistance Without using the output signal _vo as 1.2 V _pp , the load R _L
Can be supplied to

FIG. 5 shows still another embodiment of the driver circuit according to the present invention. The present embodiment is different from the above embodiments in that the driver amplifier 600 converts a voltage corresponding to a differential input into a current, amplifies the current at a predetermined amplification factor m, and outputs the amplified current. The difference is that a differential amplifier is applied.

[0048] In detail, the driver circuit according to this embodiment, as shown in FIG. 5, the non-inverting terminal of the driver amplifier 600 (+), a video signal v _i is supplied inverted terminal - bias circuit () One side of the feedback circuit 300 is connected to 200 and the other side of the feedback circuit 300 forms a non-inverting amplifier circuit connected to the output terminal 18. Further, the output is connected to a predetermined cable 500 via a coupling capacitor 400 to supply a predetermined output signal to the load _RL .

The driver amplifier 600 has an input stage formed by a voltage / current conversion circuit for current-converting the voltage of the differential input from the non-inverting terminal and the inverting terminal with a predetermined conversion coefficient. the current from the circuit is a two-stage configuration of a differential amplifier formed by the current conversion circuit for amplifying with a predetermined amplification factor, the predetermined conversion resistor R _E to determine the conversion factor in voltage-current conversion circuit connected Have been.

More specifically, for example, as shown in FIG. 7, the voltage-current conversion circuit includes a first buffer circuit 50 formed by transistors Q602 to Q608, and a transistor Q6.
And a second buffer circuit 52 formed by 10～Q616, respective outputs are connected in common at conversion resistor R _E. Each of the buffer circuits 50 and 52 is formed by a two-stage push-pull type voltage follower circuit similar to the buffer circuit 10 of the embodiment shown in FIG. Are connected, and the inverting terminal is connected to the input of the second buffer circuit 52. Each of the circuits 50 and 52 amplifies the input voltage with a gain of 1, and the difference voltage is applied to the conversion resistor _RE , and a current corresponding to the value is supplied to the current amplifier circuit.

The current amplifying circuit is a current mirror circuit formed by four transistors Q618 to Q624, similarly to the current amplifying circuit 12 of the embodiment shown in FIG. The transistors Q618 and Q620 are connected to the transistors Q606 and Q608 of the first buffer circuit 50, respectively, so that the respective collector currents are supplied to the transistors Q62 and Q62 in the subsequent stage.
2, Supply to Q624. Subsequent transistors Q622, Q624
Outputs an output signal, which has been current-amplified at a predetermined amplification factor m, to an output terminal 18 from a commonly connected collector.

Returning to FIG. 5, in the driver circuit of this embodiment, when a video signal is supplied to the non-inverting terminal (+),
The input voltage v _i and the inversion terminal (-) differential voltage between the input voltage v _f in is converted into a current corresponding to the value of the conversion resistor R _E, is further amplified with a predetermined amplification factor m, the output Output from terminal 18. At that time, the output current i _p is expressed by the following equation (15).

[0053]

[Number 11] _{i p = (v i -v f} ) · G m ··· (15) However, the G _m = _m / R _E.

[0054] Input voltage v _f to this time, the inverting terminal is determined by a feedback resistor R2 and the resistor R1 of the feedback circuit 300, when the voltage of the output terminal 18 and v _o, represented by the following formula (16) .

[0055]

V _f = {R1 / (R1 + R2)} · _vo (16) The output current i _p is a feedback current i _f , a coupling capacitor 40
Assuming that the output current to the 0 side is i _o , it is represented by the following equation (17), and the feedback current _if is represented by the following equation (18).

[0056]

[Number 13] _{i p = i f + i o} ··· (17) i f = (v o -v f) / R2 ··· (18) As a result, the present embodiment from the above equation (15) to (18) The output voltage _vo of the example driver circuit is expressed by the following equation (19).

[0057]

Equation 14] _{v o = {G m · (} R1 + R2) / (1 + G m · R1)} v i - {(R1 + R2) / (1 + G m · R1)} i o ··· (19) Thus, each similar to the embodiment, the overall gain a and an output resistor R _o of the entire circuit from the above equation (19), the following equations (2
0) and (21).

[0058]

[Number 15] _{A = G m · (R1 +} R2) / (1 + G m · R1) = m · (R1 + R2) / (RE + m · R1) ··· (20) R o = (R1 + R2) / (1 + G m (R1) = R _E (R 1 + R 2) / (R _E + m R 1) (21) As a result, in the above equations (20) and (21), for example, each value is m = 18, R _E = 680, R1 = 680, R2 = 750, it is possible to form a driver circuit with an output resistance of 75Ω, in which the total gain is almost doubled.

FIG. 6 shows a modification of the driver circuit according to the above embodiment. This embodiment is different from the above embodiment in that the non-inverting terminal of the driver amplifier 600 is
Connect the predetermined reference voltage V _R to (+), an inverting terminal (-) to the supplied video signal v _i through an input resistor R1, and outputs the output signal v _o which inverts and amplifies the input signal The point is that an inverting amplifier is formed.

That is, in the present embodiment, an inverted and amplified video signal is output to the output of the driver amplifier 600. At this time, _{if the} voltage supplied to the inverting terminal (-) is vf, the output current i _p is represented by the following equation (22).

[0061]

Equation 16] _{i p = -V f · G m} ··· (22) At this time, the input voltage v _f to the inverting terminal the feedback voltage of the output voltage v _o from the video signal v _i and the output terminal 18 and From the relationship
It is represented by (23).

[0062]

Equation 17] _{v f = {R2 / (R1} + R2)} · v i + {R1 / (R1 + R2)} · v o ··· and (23), as in the above embodiment, the output from the output terminal 18 Current
i _p is expressed by the following equation (24) and a current i _o of the coupling capacitor side and the feedback current i _f, the feedback current i _f is expressed by the following equation (25).

[0063]

Equation 18] _{i p = i f + i o} ··· (24) i f = (v o -v f) / R2 ··· (25) Therefore, the present embodiment from the above equation (22) - (25) Example The output signal v _o of the driver circuit is represented by the following equation (26).

[0064]

(19) v _o = − {(1 + G _m · R2) / (1 + G _m · R1)} v _i − {(R1 + R2) / (1 + G _m · R1)} i _o (26) similar to the above embodiments, the overall gain a and an output resistor R _o of the entire circuit from the above equation (26), the following equations (2
7), (28).

[0065]

A = (1 + _Gm · R2) / (1 + _Gm · R1) = ( _RE + m · R2) / ( _RE + m · R1) (27) _Ro = (R1 + R2) / (1 + _Gm · R1) = _RE · (R1 + R2) / ( _RE + m · R1) (28) As a result, in the above equations (27) and (28), for example, each value is set to R2 = 750. , R _E = R1 = 360, m = 14, it is possible to form a driver circuit having an output resistance of 75Ω, in which the total gain is almost doubled.

In each of the above embodiments, 1.2 Ω load was applied to a 75Ω load.
Although the case where the present invention is applied to an output circuit that supplies a video signal having a signal amplitude of V _pp has been described as an example, in the present invention,
The present invention is not limited to this, and may be applied to any case when supplying or driving a signal to a desired load or circuit.

Further, in each of the above embodiments, an example has been described in which the driver amplifiers are each configured by a bipolar transistor. However, in the present invention, a MOS transistor may be applied.

[0068]

As described above in detail, according to the driver circuit of the present invention, a current corresponding to the voltage of an input signal is obtained at the input stage, and the current is output at a predetermined amplification factor at the output stage. The output is negatively fed back to the input side with a predetermined feedback resistor to the current output type amplifier that amplifies and outputs, and the output gain and output resistance of the entire circuit are determined based on the value of the feedback resistor and the current amplification factor. Since the desired value is set, the output dynamic range can be reduced in the terminated state. Therefore, the power supply voltage can be reduced, and the power supply circuit and the like can be reduced in size and the cost of the device can be reduced.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of a driver circuit according to the present invention.

FIG. 2 is a circuit configuration diagram showing a more specific embodiment of the driver circuit according to the embodiment of FIG.

FIG. 3 is a circuit diagram showing a modification of the driver circuit according to the embodiment of FIG. 1;

FIG. 4 is a circuit configuration diagram showing a more specific embodiment of the driver circuit according to the embodiment of FIG. 3;

FIG. 5 is a circuit diagram showing another embodiment of the driver circuit according to the present invention.

FIG. 6 is a circuit diagram showing a modified example of the driver circuit according to the embodiment of FIG. 5;

FIG. 7 is a circuit configuration diagram showing a more specific embodiment of the driver circuit according to the embodiment of FIG. 5 or FIG. 6;

FIG. 8 is a circuit configuration diagram showing an equivalent circuit of the driver circuit according to the embodiment of FIG. 1;

FIG. 9 is a circuit configuration diagram showing a comparative example for clarifying the effect of the driver circuit according to the present invention.

FIG. 10 is a circuit configuration diagram showing a comparative example for clarifying the effect of the driver circuit according to the present invention.

FIG. 11 is a circuit configuration diagram showing a comparative example for clarifying the effect of the driver circuit according to the present invention.

[Explanation of symbols]

 10 Buffer circuit 12 Current amplifier circuit 100, 600 Driver amplifier R1 Bias resistor R2 Feedback resistor

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Naoki Kubo 3-11-46 Izumi, Asaka-shi, Saitama F-term in Fujisha Shin Film Co., Ltd. 5C021 PA03 PA04 PA06 PA95 RC03 XA03 XA19

Claims (8)

[Claims] 1. A driver circuit for amplifying an input signal to a predetermined signal amplitude and supplying the amplified signal to a load, the circuit comprising: buffer means for obtaining a voltage and a current corresponding to the input signal; Current amplification means for amplifying and outputting a current at a predetermined amplification factor, and feedback means for performing negative feedback from an output terminal of the current amplification means to an output terminal of the buffer means via a predetermined feedback resistor; The signal gain and output resistance of the entire circuit are set to desired values based on the current amplification factor of the current amplifying means and the resistance value of the feedback means, and the signal is amplified to a desired signal amplitude from the output terminal of the current amplifying means. A driver circuit for supplying the output signal to a load. 2. The circuit according to claim 1, wherein the buffer means includes a voltage follower circuit that amplifies a voltage applied to the first terminal with a gain of “1” and outputs the amplified voltage to a second terminal. The current amplifying means is mirror-connected so as to detect an output current of the voltage follower circuit, and a feedback of the feedback means is provided between an output terminal of the current amplifying means and a second terminal of the buffer means. A driver circuit to which a resistor is connected. 3. The circuit according to claim 2, wherein an input signal is supplied to a first terminal of said buffer means, and a predetermined bias is applied to said second terminal. A non-inverting amplifier which non-invertingly amplifies an input signal from a terminal of (i) and supplies the amplified signal to a load. 4. The circuit according to claim 2, wherein a predetermined reference voltage is applied to a first terminal of said buffer means, and an input signal is supplied to a second terminal of said buffer means.
A driver circuit, which is an inverting amplifier that inverts and amplifies an input signal from a terminal of (1) and supplies the signal to a load. 5. A driver circuit for amplifying an input signal to a predetermined signal amplitude and supplying the amplified signal to a load, wherein the circuit is voltage-current conversion means for converting a voltage corresponding to the input signal into a current, and comprising a non-inverting terminal. Voltage-current conversion means for converting a differential voltage between the voltage and the inverting terminal into a current with a predetermined conversion coefficient, and current amplification for amplifying and outputting the current obtained by the voltage-current conversion means at a predetermined amplification factor Means, and feedback means for performing negative feedback from an output terminal of the current amplifying means to an inverting terminal of the voltage / current converting means via a predetermined feedback resistor, wherein a conversion coefficient of the voltage / current converting means, The signal gain and output resistance of the entire circuit are set to desired values based on the amplification factor and the resistance value of the feedback means, and the output signal amplified to a predetermined level from the output terminal of the current amplification means is applied to the load. Supply Driver circuit which is characterized the door. 6. The circuit according to claim 5, wherein the voltage-current conversion unit is configured to obtain an output voltage corresponding to an applied voltage from a non-inverting terminal, and to respond to an applied voltage from an inverting terminal. A second buffer for obtaining an output voltage; and a conversion resistor for connecting an output of the first buffer and an output of the second buffer to obtain a current according to the differential voltage. The current amplifying means is mirror-connected so as to detect a current flowing through one buffer output, and a feedback resistor of the feedback means is connected between an output of the current amplifying means and an inverting terminal of the second buffer. A driver circuit characterized in that: 7. The circuit according to claim 6, wherein an input signal is supplied to a non-inverting terminal of the voltage-current converting means, and a predetermined bias is applied to the inverting terminal.
A driver circuit, which is a non-inverting amplifier that non-invertingly amplifies an input signal from a non-inverting terminal and supplies the amplified signal to a load. 8. The circuit according to claim 6, wherein a predetermined reference voltage is applied to a non-inverting terminal of the voltage-current converting means, an input signal is supplied to an inverting terminal, and A driver circuit, which is an inverting amplifier that inverts and amplifies the input signal of (1) and supplies it to a load.