JPH0440886B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a balanced transformerless (hereinafter abbreviated as BTL) amplifier.

BTL amplifiers are used as amplifiers that can obtain high output with low power supply voltage.

A conventional BTL amplifier includes, for example, as shown in FIG. 1, a first power amplifier 4 consisting of an inverting amplifier 1, a voltage amplification stage 2, and a current amplification stage 3, and a second power amplifier configured similarly to the first power amplifier. The disadvantage is that the amplifier 5 is required, the number of parts is large, and the circuit is complicated. Note that 6 is a speaker as a load.

The present invention has been made in view of the above, and it is an object of the present invention to eliminate the above-mentioned drawbacks and provide a BTL amplifier with a small number of parts and a simple circuit configuration.

The present invention will be explained below with reference to Examples.

FIG. 2 is a circuit diagram of one embodiment of the present invention.

10 is a voltage amplification stage, 11 and 12 are current amplification stages driven by the output and inverted output from the voltage amplification stage 10 to drive the speaker 6, and 13 is a negative feedback circuit.

The voltage amplification stage 10 includes a transistor Q ₁ to which an input voltage is applied, a transistor Q ₂ to which an output voltage of the negative feedback circuit 13 is applied, and a constant current source circuit I.
and a transistor that amplifies the output of the first-stage differential amplifier A, respectively.
It consists of a second stage differential amplifier B consisting of _Q3 and _Q4 . That is, the base of the transistor Q ₁ as the first input terminal (input terminal N),
The input voltage and the negative feedback circuit 13 are connected to the base of the transistor Q ₂ as the second input terminal, respectively.
An output voltage of is applied.

The current amplification stage 11 consists of complementary connected transistors Q ₅ , Q ₆ , Q ₇ and Q ₈ for current amplifying the output of the transistor Q ₄ of the second stage differential amplifier B. Further, the current amplification stage 12 includes complementary-connected transistors Q ₉ , which amplify the current of the output of the transistor Q ₃ of the second stage differential amplifier B;
It consists of Q ₁₀ , Q ₁₁ and Q ₁₂ .

On the other hand, since the signal at the output terminal E point of the current amplification stage 11 is in reverse phase with the signal at the output terminal F point of the current amplification stage 12, the negative feedback circuit 13 inverts the signal at the F point and generates the signal at the E point. This is a circuit for mixing and amplifying the mixed signals and feeding them back to the second input terminal of the first-stage differential amplifier A of the voltage amplification stage 10 as an inverting input.

When an input signal is now applied to the input terminal IN of the voltage amplification stage 10, the state of the signal at each stage is shown by a sine wave diagram in FIG.

The input signal is voltage amplified in the voltage amplification stage 10, and is taken out as a balanced output from the second stage differential amplifier B, which is the output stage. That is, a signal is generated at the output point D of the transistor Q ₃ that is in opposite phase to the signal at the output point C of the transistor Q ₄ and has exactly the same amplitude. Therefore this transistor
The output signals of Q ₃ and Q ₄ are transferred to current amplification stages 11 and 12.
By amplifying the current with , there is no need for a separate inverting amplifier, which simplifies the BTL circuit and reduces the number of components.

Furthermore, even when negative feedback is applied, the negative feedback circuit can be simplified by inverting the signal at point E with transistor _Q13 and adding it to the signal at point F, as shown in FIG.

As explained above, according to the present invention, the voltage amplification stage for amplifying the input signal is composed of a differential amplifier, and the inverted output is taken out from each transistor constituting the differential amplifier and current amplified. Unlike conventional BTL amplifiers, there is no need for a separate inverting circuit, which simplifies the circuit configuration and reduces the number of parts.

Further, unlike the conventional BTL amplifier, there is no need to apply a signal passed through an inverting amplifier to only one power amplifier to amplify the power, so there is no time delay between the two power amplifiers. Furthermore, since the potential difference between both ends of the load is detected and fed back, it is possible to match the input signal of the signal flowing to the load, and there is no need to connect an input resistor to the input terminal. This has the effect of preventing the S/N from deteriorating without increasing noise.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of a conventional BTL amplifier, FIG. 2 is a circuit diagram of an embodiment of the present invention, and FIG. 3 is a circuit diagram showing another example of the negative feedback circuit in FIG. 2. 10... Voltage amplification stage, 11 and 12... Current amplification stage, 13... Negative feedback circuit, A... First stage differential amplifier, B... Second stage differential amplifier, I... Constant current source circuit .

Claims (1)

[Claims] 1. A first differential amplifier made of differential transistors having first and second input terminals, and a second differential amplifier made of differential transistors each amplifying the output of the first differential amplifier. a voltage amplification stage, the input signal being input to the first base input terminal and voltage amplifying the input signal; and first and second differential transistors output from the differential transistor of the second differential amplifier of the voltage amplification stage. first and second current amplification stages to which the outputs are respectively input and which amplify the respective first and second outputs; a load connected between the outputs of the first and second current amplification stages; and a load connected between the outputs of the first and second current amplification stages; The output from the second current amplification stage is subtracted from the output from the current amplification stage, and this is subtracted from the output from the second differential transistor of the first differential amplifier of the voltage amplification stage.
A balanced transformerless amplifier comprising: a negative feedback circuit configured to provide negative feedback to the differential transistor by inputting it to an input terminal.