JPH11186857A - Low power output device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a low power output device where a dynamic range of its output stage is ensured with a low power supply voltage and distortion in an output signal is suppressed. SOLUTION: An inverting amplifier is configured with a pre-stage voltage amplifier circuit 100, a post-stage current amplifier circuit 200, and a negative feedback circuit 300 that feeds back an output of the current amplifier circuit 200 to an inverting input terminal of the voltage amplifier circuit 100. The voltage amplifier circuit 100 provides an output of a difference voltage between an input voltage from a signal source 400 and a bias voltage from a reference voltage Vref to a 1st resistor R103. The 1st resistor R103 converts an output voltage from the voltage amplifier circuit 100 into a current and the current amplifier circuit 200 amplifies the current based on a mirror ratio by mirror circuits 202, 204. A resistor R104 (2nd resistor) is connected between an input stage and an output stage of the mirror circuits 202, 204 to control a loop gain.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a low power output device used for an output stage amplifier for outputting, for example, an audio signal sent from a signal processing system to an audio output unit.

[0002]

2. Description of the Related Art Conventionally, for example, an amplifier as shown in FIG. 5 has been known. In this amplifier, the input signal from the input signal source 2 via the resistor R _A transistor Q _A, Q
_B, and inputs Q _C, the differential input circuit formed by Q _D. The differential input circuit, dividing resistors R _B of the reference voltage V _0, is supplied with a bias voltage by R _C, and supplies a differential output between the bias voltage and the input voltage to the transistor Q _E of the amplifier stage ing.

[0003] transistor emitter output of Q _E is supplied to the base of the transistor Q _F of the output stage, transistor Q emitter output of _F via a capacitor C load RL
Supplied to Further, the emitter of the transistor Q _F is the reference voltage V ₀ and the resistor R _B, a bias voltage by R _C are supplied.

[0004]

However, the amplifier having the above-mentioned configuration can be used only when there is a margin in the power supply voltage because the output of the amplifier uses the emitter output. Therefore, for example, such as a portable battery-powered audio device, which requires a power supply voltage of at least about 2.7 V and an output level of about -1 dBm (600Ω), an NPN transistor Q in the output stage is required.
Voltage amplification factor V _F of the _F will limit the dynamic range. Also, each transistor Q _A , Q _B , Q in the input stage
_C, because it constitutes a forward amplifiers Q _D and a resistor R _B,
The input signal swings, and the transistors Q _A ,
For Q _B, Q _C, Early effect by Q _D, has also become a cause of distortion is worse.

SUMMARY OF THE INVENTION An object of the present invention is to provide a low power output device which can secure a dynamic range of an output stage with a low power supply voltage and can suppress distortion of an output signal.

[0006]

According to the present invention, there is provided a low power output apparatus for amplifying an input voltage sent from a signal processing system and outputting the amplified input voltage to a load. A voltage amplifier circuit having an input terminal and a non-inverting input terminal for inputting a predetermined reference voltage, amplifying and outputting a difference between the input voltage signal and the reference voltage, and converting a voltage output of the voltage amplifier circuit into a current. A first resistor to convert;
A current amplifier circuit for amplifying the output current of the first resistor and outputting the amplified current to a load; a bias current supply circuit for supplying a bias current to an input terminal of the current amplifier circuit; And a negative feedback circuit that feeds back to the inverting input terminal of the voltage amplifying circuit through the negative feedback circuit. Further, according to the present invention, the current amplifying circuit has a mirror circuit for amplifying an output current of the first resistor by a mirror ratio, and a second resistor connects between an input stage and an output stage of the mirror circuit. It is characterized by being connected.

In the low power output device according to the present invention, the input signal is input to the preceding voltage amplifier circuit, and the difference between the input signal and the reference voltage is amplified and supplied to the first resistor. In the first resistor, the output of the voltage amplifying circuit is subjected to voltage-to-current conversion and supplied to the current amplifying circuit at the subsequent stage. With the first resistor, the output amplitude of the voltage amplifier circuit can be suppressed, and a sufficient dynamic range can be secured. Next, the current amplifier circuit current-amplifies the output from the first resistor. A bias current from a bias current supply circuit is supplied to an input terminal of the current amplifier circuit, and the biased amplified current is output to a load.

The output of the current amplifier circuit is fed back to the inverting input terminal of the voltage amplifier circuit via a feedback resistor, thereby forming an inverting amplifier, eliminating the fluctuation of the reference voltage with respect to the voltage amplifier circuit and reducing the output signal. Distortion can be suppressed.
The current amplifying circuit is a mirror circuit that amplifies a current by, for example, a mirror ratio. By connecting the input stage and the output stage of the mirror circuit via a second resistor, the loop gain is reduced, and the load fluctuation is reduced. In addition to suppressing the oscillation of the output stage, even when the load is light, it is possible to allow a certain amount of current to flow through the mirror circuit in the output stage, thereby obtaining a phase margin.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a low power output device according to the present invention will be described below. FIG. 1 is a block diagram showing an outline of a configuration example of a low power output device according to the present invention, and FIG. 2 is a circuit diagram showing an equivalent circuit of a current amplifier circuit at a subsequent stage of the low power output device shown in FIG. . As shown,
The low-power output device of the present example includes a voltage amplifying circuit 100 of the preceding stage.
, A current amplification circuit 200 at the subsequent stage, and a current amplification circuit 200
Inverting amplifier (EPBUF) having a negative feedback circuit 300 for feeding the output of the inverter to the inverting input terminal of the voltage amplifying circuit 100
Is configured as

[0010] voltage amplification circuit 100, an input voltage sent from the signal source (signal processing system) 400 inverting input terminal through a resistor R101 (-) as well as input to the bias voltage by the reference voltage V _{re f} The differential voltage of the voltage supplied to the non-inverting input terminal (+) and supplied to each input terminal is output from the output terminal and supplied to the current amplifier circuit 200.
The current amplifying circuit 200 includes a resistor R103 as shown in FIG.
(1st resistor) converts the output voltage from the voltage amplifier circuit 100 into a current, and amplifies the current by the mirror ratio of the mirror circuit 202 provided on the power supply Vcc side and the mirror circuit 204 provided on the ground GND side. It is.

On the input side of each of the mirror circuits 202 and 204 of the current amplifying circuit 200, a reference voltage V _ref , transistors Q01, Q02, Q03, Q04 and a constant current source 410,
420 supplies a center bias current.
Further, each of the mirror circuits 202 and 20 of the current amplifying circuit 200
A resistor R104 (second resistor) is connected between the input stage and the output stage. The output stage of each of the mirror circuits 202 and 204 of the current amplification circuit 200 is connected to the load RL via the capacitor C. Further, the output stage of each of the mirror circuits 202 and 204 of the current amplifying circuit 200 is connected to the inverting input terminal (-) of the voltage amplifying circuit 100 via the feedback resistor R102.

In the inverting amplifier having the above configuration, the amplifier gain A is determined by the resistors R101 and R102.
R102 / R101. By configuring such an inverting amplifier, even if the input signal swings, the resistance R101
Since the reference voltage side does not fluctuate due to the imaginary short circuit caused by the path of the resistor R102 and the resistor R102, the Early effect of the transistors of the differential pair constituting the input stage of the voltage amplifying circuit 100 cannot be seen, which is advantageous for distortion.

FIG. 3 is a circuit diagram showing a more detailed equivalent circuit configuration of the low power output device as described above. Less than,
The detailed operation of this example will be described with reference to FIG.
First, the configuration of the voltage amplification circuit 100 in the preceding stage will be described. This voltage amplifying circuit 100 performs a class AB operation, and an input stage is constituted by transistors Q1 to Q4. Then, a resistor R1 (R101) is input from the input terminal in.
The difference output between the input voltage input to the base (inverting terminal) of the transistor Q2 via the input terminal bi and the bias voltage input from the input terminal bi to the base (non-inverting terminal) of the transistor Q1 via the resistor R2 is output to the transistor Q5. Output.

The difference output output to the transistor Q5 is transmitted to the output stage transistors Q9 and Q10 by a mirror circuit composed of transistors Q6 and Q7 and gained by a resistor R6. Transistors Q9, Q
Numeral 10 is for performing a push-pull operation. In order to allow a bias current to flow, resistors R4 and R5 and a transistor Q
8, a voltage of 2V _F is given.

The resistors R4 and R5 and the transistor Q8 are
Purpose of improving crossover distortion of signals output to transistors Q9 and Q10, and
10 is provided for the purpose of reducing the idling current by the resistance values of the resistors R4 and R5. The difference voltage output from the transistors Q9 and Q10 is equal to the resistance R
8 (resistor R103). Resistance R8
At the connection point α of the input stage of the current amplification circuit 200,
A current corresponding to a change in signal flows through the resistor R8 and is supplied to the current amplification circuit 200 in the next stage. Further, by reducing the resistance value of the resistor R8, the output amplitude of the transistors Q9 and Q10 is suppressed, and the dynamic range of the voltage amplifier circuit 100 is secured.

The current amplifying circuit 200 includes a transistor Q1
7, Q21 and transistors Q20, Q22 constitute a mirror circuit, and a current is gained by this mirror ratio, and an output terminal o
Sufficient current is supplied to the load RL connected to ut. The bias current flowing through the transistors Q18 and Q19 (transistors Q03 and Q04)
11 and 12 (transistors Q01 and Q02) are multiplied and the base-emitter voltage V _BE is increased to reduce the idling current of the transistors Q18 and Q19.

The transistor Q16 is a current source for the base current I _B guarantee the mirror circuit of the PNP transistor Q17, Q21, when the transistor Q21 is current flow, increasing the current of the transistor Q16, the base current I _B of the transistor Q21 To be able to pull enough. The output stages of the mirror circuits 202 and 204 are PN
A connection point β between the collector of the P transistor Q21 and the collector of the NPN transistor Q22 was set as the output terminal out.
A so-called collector matching circuit is formed. With the collector output type, the power supply voltage V
It is possible to output a voltage obtained by subtracting the saturation voltages Vsat1 and Vsat2 of the transistors Q21 and Q22 from cc.

The output terminal out is connected to a feedback resistor R7.
It is connected via (R102) to the base of the transistor Q2, which is the inverting terminal. Further, a resistor R13 (resistance 104) is provided between the input stage and the output stage of the current amplification circuit 200. This resistor R13 lowers the loop gain so as not to oscillate due to the fluctuation of the load RL (open to 128Ω). Even when the load RL is light, the current on the output stage side of the mirror circuit flows to some extent, and a phase margin can be obtained. It is like that.

With the above configuration, a low-voltage, low-impedance load can be driven. Further, low power consumption can be achieved by such a low voltage and the above-described AB class operation. Further, as described above, by adopting the configuration of the inverting amplifier, the reference voltage does not fluctuate and distortion can be improved.

The above-described low power output device is, for example, an 8 mm video tape recorder. When recording a video signal, the audio signal input from a microphone or the like is subjected to a level limiting process or a noise removing process, and then is subjected to FM modulation. A recording / reproducing circuit (audio FM) which reproduces the recorded audio signal by FM demodulation and reproduces the same when reproducing a video signal, and outputs the signal to headphones or the like.
System). FIG. 4 is a block diagram showing a configuration of a recording system in such an audio FM system.

In FIG. 4, during recording of an audio signal, an audio signal input from a microphone (not shown) is subjected to level limiting processing by an automatic level controller (ALC) 10 and passed through an amplifier 12 to an audio bandpass filter circuit (LPF). After the frequency of 30 KHz or more is cut off by 14), it is input to the DC circuit 16. The DC circuit 16 performs offset correction on input audio signals with respect to variations in characteristics between elements and the like, and performs bias adjustment corresponding to a power supply voltage.

The audio signal output from the DC circuit 16 is supplied to a matrix circuit (MATRIX) 18,
Through an FM processing system composed of a noise reduction circuit (NR) 20 and a modulation circuit (MOD) 22,
The data is transmitted to a recording / reproducing mechanism (not shown) and recorded on an 8 mm tape. The audio signal output from the DC circuit 16 is sent to a headphone amplifier (output stage amplifier) 26 and output from a headphone (not shown). The headphone amplifier 26 is configured by the low power output device shown in FIGS.

On the other hand, at the time of reproducing the audio signal, the FM-modulated audio signal reproduced from the tape by the recording / reproducing mechanism is demodulated through a path of a demodulation circuit, a noise reduction circuit 20, and a matrix circuit 18 (not shown). Is output to the headphone amplifier 26 through the DC circuit 18.

In such an audio FM system,
The audio signal sent from the DC circuit 16 is converted into a current output that has good output distortion characteristics and is effective for securing a dynamic range by the above-described low-power output device in the headphone up 26, and drives the load. Can be. Therefore, with the system having such a configuration, a large dynamic range can be secured at a low voltage, and for example, a signal of a level of −1 dBm (600Ω) can be output at a power supply voltage of 2.7 V.

As a conventional audio FM system, a headphone amplifier is connected to a high-level (for example, 5 V) first
There is also provided a configuration that achieves low power consumption by driving with a low-level (for example, 3 V) second power source while driving most other circuits with a low-level (for example, 3 V) second power source. However, in this configuration, in the DC circuit, it is necessary to apply two types of bias voltages corresponding to the first power supply and the second power supply, and distribute the signals to the headphone amplifier side and the signal processing system side. Accordingly, there has been a problem that the circuit configuration is complicated. Therefore, by using the above-described low-power output device of the present example, it is possible to secure a good sound output by the low-voltage power supply, and therefore, a path of the amplifier to the sound output unit and another signal processing system are required. A device driven by a single power supply can be configured, and power consumption can be reduced and the circuit configuration can be simplified.

In the above example, the present invention is applied to audio F
Although the case of application to the M system has been described, the present invention is not limited to this, and is widely applied to various low power output devices having an output stage amplifier for outputting an audio signal to an audio output unit using a low voltage power supply. Can be done. Also,
As a configuration similar to the above-described low-power output device, for example, a configuration disclosed in Japanese Patent Application Laid-Open No. 63-285004 is known, but the low-power output device of the present embodiment employs the above-described operation of the resistor R8. The output amplitude of the voltage amplifying circuit is suppressed, a sufficient dynamic range is secured, and the resistance R1
Due to the effect of 3, there is a remarkable difference in that a phase margin in the current amplifying circuit can be obtained with respect to load fluctuation.

[0027]

As described above, in the low power output device of the present invention, the input voltage sent from the signal processing system is amplified by the preceding voltage amplifier circuit, and this is converted into a current by the first resistor. After conversion, the current is further amplified by the current amplifier circuit and supplied to the load, and the output of the current amplifier circuit is negatively fed back to the voltage amplifier circuit. Therefore, it is possible to drive a low-impedance load with low power, secure a dynamic range of input even at low voltage, and further improve signal distortion.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an outline of a configuration example of a low power output device according to the present invention.

FIG. 2 is a circuit diagram showing an equivalent circuit of a current amplifier circuit at a subsequent stage of the low power output device shown in FIG.

FIG. 3 is a circuit diagram showing a more detailed equivalent circuit of the low power output device shown in FIG. 1;

FIG. 4 is a block diagram showing a configuration of a recording system in an audio FM system provided with the low power output device shown in FIG.

FIG. 5 is a circuit diagram showing a configuration example of a conventional amplifier.

[Explanation of symbols]

100: voltage amplification circuit, 200: current amplification circuit, 2
02, 204: mirror circuit, 300: negative feedback circuit,
400 ... signal source.

Continuation of the front page (72) Inventor Sachi Kobayashi 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Sachie Yoshizawa 6-35, Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Corporation In-company (72) Inventor Masaki Yoshihara 5-1 Noguchikita, Kokubu-shi, Kagoshima Prefecture Inside Sony Kokubu Corporation (72) Inventor Kazue Toguchi 5-1 Noguchikita, Kokubu-shi, Kagoshima Sony Kokubu Corporation

Claims (4)

[Claims] 1. A low-power output device for amplifying an input voltage sent from a signal processing system and outputting the amplified voltage to a load, wherein an inverting input terminal for inputting the input voltage and a non-inverting input terminal for inputting a predetermined reference voltage. A voltage amplifier circuit that amplifies and outputs a difference between the input voltage signal and a reference voltage; a first resistor that converts a voltage output of the voltage amplifier circuit into a current; A current amplifier circuit that amplifies an output current and outputs the amplified current to a load; a bias current supply circuit that supplies a bias current to an input terminal of the current amplifier circuit; and a voltage amplifier that outputs a current output of the current amplifier circuit via a feedback resistor. And a negative feedback circuit for feeding back to an inverting input terminal of the circuit. 2. The current amplifier circuit according to claim 1, further comprising a mirror circuit configured to amplify an output current of the first resistor by a mirror ratio, and to connect between an input stage and an output stage of the mirror circuit via a second resistor. The low power output device according to claim 1, wherein the output device is connected. 3. The low power output device according to claim 1, wherein the current amplification circuit has an output stage of a collector output type. 4. The apparatus according to claim 1, wherein the input voltage is an audio signal sent from a signal processing system, and the load is an audio output unit for outputting the audio signal as audio. Low power output device.