JPH07193439A - Amplifier part - Google Patents

Abstract

PURPOSE:To obtain an amplifier for obtaining a line driver circuit, which is small in both distortion and power consumption, regarding an amplifier part. CONSTITUTION:AB and +B class push-pull characteristics are obtained by performing a connection by using amplifiers 1 and 2, constant current sources 3 and 4, a one-conduction type transistor Tr 1, a one-conduction type transistor Tr 3 whose gate is connected with reference voltage 5, an opposite conductive type transistor Tr 2 and an opposite conductive type transistor Tr 4 whose gate is connected with reference voltage 6. Further, by applying a negative feedback, an amplifier small in distortion and power consumption is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an amplifying section used for constructing a line driver circuit (low impedance driving amplifier) for amplifying and outputting an analog signal on a transmission line.

An example of a system using a line driver circuit will be described. FIG. 9 is a block diagram of a subscriber line transmission system using an example line driver circuit.

The subscriber line transmission system shown in FIG. 9 has a digital line terminating unit 21 connected to both ends of a subscriber line 24 of a two-wire metallic cable on the station side and a digital line on the subscriber's home side. The terminal unit 20 is connected to enable bidirectional digital transmission.

The digital line termination units 20 and 21 have a line termination unit 22 and a line termination unit 23, respectively.
Includes a line driver circuit 3 that amplifies and outputs a transmission signal.
0, hybrid 31 and waveform equalization, timing extraction,
The receiver 32 has an echo canceller and the like.

The line driver circuit 30 is used in such a place, and in this case, two lines are required for each subscriber, so that the line driver circuit 30 can be made into an LSI, has a small distortion, and consumes a small amount of power. Is desired.

[0006]

2. Description of the Related Art FIG. 10 is a block diagram of a conventional line driver circuit. In the line driver circuit of FIG.
A negative feedback amplifier 13 that amplifies the input analog signal by class A with the voltage VR as the center of amplitude, and the input analog signal with the voltage VR as the center of amplitude by the amplifier 13
And a negative feedback type amplifier 14 that performs class A amplification in the opposite phase, and the outputs of the amplifiers 13 and 14 are connected to both ends of the transformer T and the amplified signal with less distortion is output from the transformer T. .

[0007]

However, since the amplifiers 13 and 14 operate in class A, there is a problem that the power consumption is large.

It is an object of the present invention to provide an amplifier for obtaining a line driver circuit which has low distortion and low power consumption.

[0009]

In order to obtain an amplifier with low power consumption, a method of using an amplifier having a class B push-pull characteristic shown in FIG. 6A can be considered, but it is realized by using a transistor of LSI. In this case, since power consumption increases when an offset voltage is generated due to variations in the characteristics of the transistors used, it is necessary to widen it to some extent as in the dead zone shown in FIG.

If there is a dead zone, even if negative feedback is applied to reduce the distortion, the gain becomes 0 in the dead zone and a crossover distortion occurs in which a part of the signal is lost. In order to reduce the crossover distortion, it is advisable to perform the AB class operation in the dead zone as shown in FIG. 6 (B).

However, since a broken line portion between the class AB and the class B causes distortion, a characteristic as shown by a dotted line in FIG. 6 (B) is obtained by applying negative feedback, and amplification of low distortion and low power consumption is achieved. Part is obtained.

In order to obtain the class AB + class B push-pull characteristics shown in FIG. 6 (B) and apply negative feedback to realize an amplifier section which can obtain the characteristics shown by the dotted line in FIG. 6 (B), As shown in the block diagram of the amplifier section of the embodiment of the present invention, a first conductivity type first transistor Tr1 and a second conductivity type second transistor Tr2 are connected in series between the power supply voltage and the ground. A circuit that outputs the connection point and the first constant current source 3
A circuit in which a third transistor Tr3 of one conductivity type having the first reference voltage 5 connected to the gate is connected in series, and a fourth transistor Tr4 of the opposite conductivity type having the second reference voltage 6 connected to the gate And a circuit in which the second constant current source 4 is connected in series are inserted, and the analog signal to be input is
The output of the first amplifier 1 is connected to the gate of the first transistor Tr1, and the first constant current source 3 and the third transistor are input to the second amplifiers 1 and 2. The output of the second amplifier 2 is connected to the connection point with Tr3, the output of the second amplifier 2 is connected to the gate of the second transistor Tr2, and the connection between the fourth transistor Tr4 and the second constant current source 4 is connected. Bias of the central voltage V1 of the amplitude of the first and second amplifiers 1 and 2 connected to the point and via the resistor R1 from the connection point of the first transistor Tr1 and the second transistor Tr2. Negative feedback is applied to the applied input.

[0013]

Function: The power supply voltage is 5V, and the amplitude center voltage V1 is 2.4.
V, the transistors Tr1 and Tr3 of one conductivity type are P-channel MOSFETs, and the transistor T of the opposite conductivity type is
The r2 and Tr4 will be described below as N-channel MOSFETs.

The input voltage becomes higher than the center voltage V1, the sink current from the power source of the first amplifier 1 becomes large,
The current Iref of the constant current source 3 is made equal to the sink current I ₀ when the output voltage becomes a voltage corresponding to the point A in FIG. 6A at the end of the dead zone, and the reference voltage 5 is set to 1
When the output voltage of the amplifier 1 becomes the voltage corresponding to the point A in FIG. 6A at the end of the dead zone, the voltage is set so that no current flows in the transistor Tr3.

The input voltage increases toward the lower side of the center voltage V1, the discharge current from the power source of the second amplifier 2 increases, and the output voltage becomes a voltage corresponding to the point B of FIG. 6A at the end of the dead zone. The current Iref of the constant current source 4 is set to be equal to the discharge current I ₀ ′ when the output voltage of the second amplifier 2 becomes _zero , and the reference voltage 6 is set at the end of the dead band of the output voltage of the second amplifier 2.
A voltage is set such that no current flows in the transistor Tr4 when the voltage corresponding to the point (A) is reached (the voltage of the reference voltage 5 becomes equal to the voltage between the drain and the gate of the transistor Tr4).

In this way, the input voltage to the amplifier 1 increases in the positive direction and the transistor Tr3 has Ir until the output voltage reaches a voltage corresponding to the point A in FIG. 6A.
The current of ef-I ₀ flows, the output impedance of the amplifier 1 is low and the gain is small, but when the voltage exceeds the voltage corresponding to the point a, the current does not flow through the transistor Tr3, and the output impedance of the amplifier 1 becomes very high. The gain increases.

On the amplifier 2 side, a current of Iref-I ₀ 'flows through the transistor Tr4 until the input voltage increases in the negative direction and the output voltage reaches the voltage corresponding to point B in FIG. 6 (A). Although the output impedance of the amplifier 2 is low and the gain is small, when the voltage becomes equal to or higher than the voltage corresponding to the point B, no current flows in the transistor Tr4, the output impedance of the amplifier 2 becomes very high, and the gain becomes large.

The impedance of the transistor Tr1 becomes smaller as the input voltage to the gate becomes higher, and the impedance of the transistor Tr2 becomes smaller as the input voltage to the gate becomes higher in the opposite direction.

Here, the equivalent circuit of the amplifier section will be described.
Since the amplifier 1 side and the amplifier 2 side are the same, the amplifier 1 side will be described with reference to FIG. That is, while the sink current I ₀ <the current Iref of the constant current source 3, the impedance Rs of the transistor Tr3 is small and much smaller than the output impedance R ₀ of the amplifier 1, so the equivalent circuit is shown in FIG. The amplification factor is gm1 × Rs × gm3 × RL as shown in the equation (1)
1, gm3 is the transconductance of the amplifier 1 and the transistor Tr1, and RL is the output load.) The gain is small and AB
Behave like a class.

When I ₀ > Iref, the transistor T
Since the impedance Rs of r3 is extremely high and approaches infinity, the equivalent circuit is as shown in FIG. 2B, and the gain is gm1 × R ₀ × gm3 × RL as shown in equation (2), and the gain is You will be able to perform class B movements.

Next, the transistors Tr1 and Tr2 shown in FIG.
3A is cut off to form a circuit as shown in FIG. 3A (constant current sources 3 and 4 and transistors Tr3 and Tr4 are not shown), and a DC voltage is input to the input.
When the voltages at points Vpo and Vno in (A) are obtained, the static characteristics shown in (a) and (b) of FIG. 3 are obtained.

Next, as shown in FIG. 4A, when the connection points of the transistors Tr1 and Tr2 are connected, a DC voltage is input to the input, and the voltage at the point of Vo is obtained, the static characteristics shown in FIG. 4 are obtained. .

That is, the dead zone is about 2.41V to 2.39V.
Is between AB and 2.41V or less and 2.39V or more is B
It has a push-pull characteristic that indicates a grade. Next, as shown in FIG. 5A, a bias of 2.4 V which is the center voltage of the amplitude of the amplifiers 1 and 2 is applied from the connection point of the transistors Tr1 and Tr2 through the resistor R1 (5 KΩ). When negative feedback is applied to the input, the voltage at the connection point has a substantially linear static characteristic as shown in FIG. 5, and the desired characteristic shown by the dotted line in FIG. 6B can be obtained.

[0024]

FIG. 1 is a block diagram of an amplifier section of an embodiment of the present invention, FIG. 7 is a block diagram of a line driver circuit of an embodiment of the present invention, and FIG. 8 is a circuit diagram of a line driver circuit of an embodiment of the present invention. Is.

In FIG. 1, the transistors Tr1 and Tr3 are P
The channel MOSFETs, the transistors Tr2 and Tr4 are N-channel MOSFETs, the amplifiers 1 and 2 are operational amplifiers, the power supply voltage is 5V, and the amplitude center voltage is 2.
Assuming that the static voltage is 4V, as described above, the negative pull is applied to the AB-class + B-class push-pull characteristics shown in FIG. 4, and the center voltage shown in FIG. It has extended static characteristics.

Therefore, when an AC signal is input to the input, an output with low power consumption and little distortion can be obtained. FIG. 7 shows a fully differential line driver circuit, which includes POSTAMP11-1,
12-1, the transistors Tr1-1, Tr2-1, the resistor R1-1, and the POSTAMPs 112-2, 12-2, the transistors Tr1-2, Tr2-2, and the resistor R1-2, the amplifying unit shown in FIG. 5, respectively. Are configured.

Further, signals of opposite phases are inputted to the input IM and IP, respectively, and the preamplifier 7 outputs signals of which the phases are inverted, one of the signals being POSTAMP 11-1, 1
2-1 and the other signal is input to the POSTAMP 11-2 and 12-2 side, and the transistors Tr1-1 and T
OP point of output of connection point of r2-1 and transistor Tr
Amplified outputs are obtained from the OM points of the outputs of the connection points of 1-2 and Tr2-2, and the voltage between the OP and OM points is output to, for example, the subscriber line via the transformer.

Further, in order to stabilize the center voltage of 2.4 V in the line driver circuit, the center voltage of 2.4 V between OP and OM points is obtained by using resistors R2 and R3 of 10 KΩ, and this voltage is calculated. , A comparator 8 having a reference voltage of 2.4V
To the preamplifier 7 and the capacitor C5.
Negative feedback is applied to the two outputs of the preamplifier 7 via the resistor R7, the capacitor C6, and the resistor R8.

Since the desired gain is 1.7 times 4.6 dB, the resistors R4 and R5 are set to 17 KΩ and the resistors R9 and R10 are set.
Is set to 10 KΩ and negative feedback is applied. That is, by using the amplifier of the present invention, a line driver circuit with low power consumption and little distortion can be configured.

FIG. 8 is a circuit diagram corresponding to the block diagram of FIG. 7, and those having the same function are indicated by the same symbols.
The one corresponding to ref is Vb of the bias circuit. The above is a P-channel MOSFET, N-channel M as one conductivity type transistor and opposite conductivity type transistor.
Although it has been described using the OSFET, the PNP transistor,
NPN transistors may be used.

[0031]

As described in detail above, according to the present invention, it is possible to construct a line driver circuit with low power consumption and little distortion.

[Brief description of drawings]

FIG. 1 is a block diagram of an amplification unit according to an embodiment of the present invention,

FIG. 2 is a diagram showing an equivalent circuit and a gain of the amplifier section of FIG.

FIG. 3 is a diagram showing static characteristics of a single amplifying section,

FIG. 4 is a diagram showing static characteristics of an amplifier of one example when negative feedback is not applied;

FIG. 5 is a diagram showing static characteristics of an example amplification section;

FIG. 6 is a characteristic diagram of a class B push-pull, class B + AB class push-pull of one example,

FIG. 7 is a block diagram of a line driver circuit according to an embodiment of the present invention,

FIG. 8 is a circuit diagram of a line driver circuit according to an embodiment of the present invention,

FIG. 9 is a block diagram of a subscriber line transmission system using an example line driver circuit;

FIG. 10 is a block diagram of a conventional line driver circuit.

[Explanation of symbols]

1, 2, 13, 14 are amplifiers, 3 and 4 are constant current sources, 5 and 6 are reference voltages, 7 is a preamplifier, 8 is a comparator, 11-1, 11-2, 12-1 and 12-2 are POSTA
MP, 20, 21 are digital line terminating units, 22 are line terminating units, 23 are line terminating units, 24 is a subscriber line, 30 is a line driver circuit, 31 is a hybrid, 32 is a receiving unit, R1, R1-1, R1-2, R2-R10, R12-R
Reference numeral 14 is a resistor, C1 to C7 are capacitors, and T is a transformer.

Claims (1)

[Claims] 1. A first of one conductivity type is provided between a power supply voltage and ground.
Circuit (Tr1) and a second transistor (Tr2) of opposite conductivity type are connected in series, and the connection point serves as an output, a first constant current source (3), and a first gate at the gate. A circuit in which a third transistor (Tr3) of one conductivity type connected to the reference voltage (5) is connected in series, and a fourth transistor (Tr4 of the opposite conductivity type in which the second reference voltage (6) is connected to the gate). ) And a circuit in which a second constant current source (4) is connected in series, and an analog signal to be input is input to the first and second amplifiers (1, 2). The output of the first amplifier (1) is connected to the first transistor (T
r1) and the connection point of the first constant current source (3) and the third transistor (Tr3), and the output of the second amplifier (2) The second transistor (Tr2) is connected to the gate of
Connected to a connection point between the second transistor (Tr4) and the second constant current source (4), and the first transistor (Tr4).
1) and the second transistor (Tr2) via a resistor (R1) from the connection point between the first and second amplifiers (1, 2)
2. An amplifier section characterized in that a negative feedback is applied to an input to which a bias of an amplitude center voltage (V1) is applied.