JPH04242307A - Amplifier circuit - Google Patents

Abstract

PURPOSE:To eliminate a feedback terminal and an externally mounted capacitor for the amplifier circuit. CONSTITUTION:Load resistors 7, 8 of a differential amplifier 50 having an operating constant current source 13 is connected to a DC voltage source 17, a series connection comprising a PNP transistor (TR) 3 (4) for level shift, a diode 15 (16) and a resistor 9 (10) is connected to a base of a PNP TR 1 (2), and a resistor 11 determining an input impedance and an input terminal 23 are connected to a base of a PNP TR3. A 1st (2nd) output of a differential amplifier 50 is connected to a noninverting input of a negative feedback amplifier circuit 19 (20) having feedback resistors 27, 28 (29, 30) and one terminal of the feedback resistors 28, 30 is connected to a DC voltage source 18.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an amplifier circuit, and in particular,
Balanced Transformer-less
This invention relates to an amplifier circuit of the s (usually referred to as BTL, and this abbreviation will be used hereinafter) type.

0002

[Prior Art] The so-called BTL type amplifier circuit is divided into two types.
By using a pair of amplifiers, driving the signals at the output of each amplifier so that the phases are opposite to each other, and connecting a load between the output terminals, an output voltage twice as high as that of a single amplifier is supplied to the load. This is an amplifier configured so that it can extract four times as much power signal as a single amplifier if the load impedance is the same.

An example of such a conventional BTL type amplifier circuit has a circuit configuration as shown in FIG.

In FIG. 3, this circuit includes resistors 157,
Load resistors 159 and 160 are connected to the collectors of PNP transistors 151 and 152, whose emitters are commonly connected to a constant current source 163 via 158, and the PNP transistor 1
A differential amplifier 150 whose first and second outputs are the collectors of 51 and 152, and PNP transistors 153 and 15.
4,155,156, and diode 169,170
, 171, 172, and constant current sources 162, 164, 1
65, 166 and the first output of the differential amplifier 150 as input, and a feedback resistor 18.
5,186, a second negative feedback amplifier circuit 174 which takes the second output as input and has feedback resistors 187, 188, and a constant current source 1 for setting the midpoint.
67, 168, capacitors 183, 184, and terminals 181, 182.

In this circuit, when a signal is input to the input terminal 177, the level-shifted signal is input to the differential amplifier 150, and the output of the differential amplifier 150 receives signals of opposite phases. is output, and the first and second output signals are amplified by first and second negative feedback amplifier circuits 173 and 174, respectively, and signals with opposite phases are also output to output terminal 179 and output terminal 180, respectively. Output.

[0006] Therefore, an output voltage four times that of the unit amplifier can be obtained at the load resistor 175 connected between the output terminals 179 and 180.

The constant current sources 167 and 168 are for setting the midpoints of the output terminals 179 and 180 of the first and second negative feedback amplifier circuits 173 and 174, respectively, and
3 and 184 are the first and second negative feedback amplifier circuits 1, respectively.
This is to prevent DC voltage gain from occurring in 73 and 174.

A load 175 is connected between the output terminals 179 and 180.
is connected.

[0009]

[Problem to be solved by the invention] Such a conventional BT
In the case of the L-type amplifier circuit, in order to perform signal input with a ground reference, the midpoint of the output terminal is set using a voltage increase caused by passing a direct current through a feedback resistor. Therefore, capacitors 183 and 184 are required to remove the DC voltage gain of negative feedback amplifier circuits 173 and 174. When integrated into an IC, the negative feedback amplifier circuits 173 and 174
Since feedback terminals 181, 182 and external capacitors 183, 184 are required, this has been an obstacle to miniaturization of ICs and cost reductions including external components.

[0010] An object of the present invention is to provide an amplifier circuit which eliminates the above-mentioned obstacles and eliminates the need for external capacitors.

[0011]

[Means for Solving the Problems] The configuration of the present invention is such that an input circuit includes a differential amplifier circuit, one and the other of a pair of outputs of the differential amplifier circuit are used as inputs, and one pair of outputs to which a load is connected. In the amplifier circuit, the load resistance of the differential amplifier circuit is connected to a first constant voltage source, and the load resistance of the differential amplifier circuit is connected to a first constant voltage source, and 1. One end of the feedback resistor of the second negative feedback amplifier circuit is connected to the second constant voltage source.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a circuit diagram showing an amplifier circuit according to an embodiment of the present invention.

In FIG. 1, in the amplifier circuit of this embodiment,
A DC voltage source 17 is connected to load resistors 7 and 8 of a differential amplifier 50 having a constant current source 13 for operation, and PNP transistors 3 and 4 for level shifting, diodes 15 and 16 are connected to the bases of PNP transistors 1 and 2. Resistors 9 and 10 are connected in series, and the base of the PNP transistor 3 is connected to an input terminal 23 and a resistor 11 that determines input impedance. The first and second outputs of the differential amplifier 50 are connected to feedback resistors 27, 28 and 2, respectively.
A direct current voltage source 18 is connected to the feedback resistors 28 and 30.

Note that it is sufficient for the DC voltage sources 17 and 18 to be voltage sources that can be generated inside the IC.

Furthermore, constant current sources 12, 13, 14, etc. are further provided.

In this BTL-configured amplifier circuit, the DC voltage sources 17 and 18 are set so that the voltage source 18 has a midpoint potential between the power supply terminal 22 and the ground terminal 24, and the voltage source 17 has a voltage source 18 minus the voltage drop across resistor 8, that is, PNP transistors 1 and 2.
The DC voltage of the collector of the voltage source 18 and the voltage source 18 are set to be equal.

At this time, the base potentials of the PNP transistors 1 and 2 are set higher than the voltage source 18.

The signal input to the input terminal 23 is PNP
The signal is lifted up by the transistor 3, diode 15, and resistor 9, and input to the differential amplifier 50. The first and second output signals whose gain has been increased by the differential amplifier 50 are sent to the respective first and second negative feedback amplifiers 19.
, 20.

At this time, the respective positive phase and negative phase input terminals of the first and second negative feedback amplifiers 19 and 20 are
Since they are at the same DC potential, only the signal input is amplified and output to the output terminals 25 and 26. If the resistor of the load 21 is connected, four times the power of a single amplifier can be obtained as in the conventional case.

Regarding the output stage and input level shift circuit of the negative feedback amplifier, the operation is almost the same as that of the conventional circuit shown in FIG. By biasing the feedback input sides of the second negative feedback amplifiers 19 and 20 with a voltage source, the signal input from the input terminal 12 can be performed with the ground reference as in the conventional case, and the need for a feedback terminal and an external capacitor is eliminated. disappears.

FIG. 2 is a circuit diagram showing an amplifier circuit according to another embodiment of the present invention.

In FIG. 2, this embodiment uses an NPN transistor.

In this embodiment, by connecting the differential amplifier 100 composed of NPN transistors, which is the input stage of the negative feedback amplifiers 66 and 67, and the constant current sources 60 and 61 to the DC voltage source 70, the PNP Effects similar to those of the above-mentioned embodiment configured with transistors can be obtained.

[0024]

As explained above, the present invention connects one end of the feedback resistor of the first and second negative feedback amplifiers that determine the voltage gain to a DC voltage source serving as a reference potential,
In addition, by connecting the load resistance side of the differential amplifier, which is the front stage of the negative feedback amplifier, to a DC voltage source, it is possible to reduce the number of feedback terminals and external capacitors, especially when implementing an IC, resulting in smaller size and lower cost. This has the effect of making it possible.

[Brief explanation of the drawing]

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

FIG. 2 is a circuit diagram showing an amplifier circuit according to another embodiment of the present invention.

FIG. 3 is a circuit diagram showing a conventional BTL type amplifier circuit.

[Explanation of symbols]

1, 2, 3, 4, 53, 54, 151, 152, 153
, 154, 155, 156 PNP transistor 51, 52 NPN transistor 5, 6, 7, 8
,9,10,11,55,56,57,58,59,1
57, 158, 159, 160, 161 Resistor 183, 184 Capacitor 15, 16, 63, 64, 169, 170, 171, 1
72 Diode 12, 13, 14, 60, 61, 62, 162, 163
, 164, 165, 166, 167, 168 Constant current source 17, 18, 65 Constant voltage source 19, 20, 66, 67, 173, 174 Negative feedback amplifier circuit 21, 68, 75 Load 23, 71, 177 Input terminal 22 , 69, 70, 176 Power terminal 25, 26
, 73, 74, 179, 180 output terminal 24,
72, 78 Ground terminal 81, 82 Feedback terminal

Claims (1)

[Claims] Claim 1: The input circuit includes a differential amplifier circuit, one of the pair of outputs of the differential amplifier circuit and the other is input, and the load is connected to one and the other of the pair of output terminals. In the amplifier circuit, the load resistance of the differential amplifier circuit is connected to a first constant voltage source, and the load resistance of the differential amplifier circuit is connected to a first constant voltage source. An amplifier circuit characterized in that one end of a feedback resistor is connected to a second constant voltage source.