Patent Application
20190149106
The present invention relates to an output circuit of an amplifier for amplifying acoustic signals, particularly to an output circuit of an analog signal amplifier, wherein the consumption current stays nearly constant.
In the field of output circuits for analog signal amplifiers, the power source circuit has a great influence on sound quality. It is widely believed that preventing flow of signal current into the power source circuit is important. (Non-patent document 1)
In an emitter follower circuit, which is a common output circuit, the consumption current changes similarly to the output current and flows into the power source of the circuit. In a two power-sourced complementary emitter follower circuit having a positive and a negative power supply, which is widely used in audio power amplifiers, the consumption current changes in a further complicated way in correlation to the output current.
Among researches on power source circuits, some in the field of specific amplifier circuits have aimed at improving sound quality by keeping the consumption current constant, but no continuing studies have been made. (Non-patent document 2)
In a conventional analog amplifier for audio use, the consumption current of the output circuit changed in correlation with the output signal. This change was unavoidable.
The present invention aims at providing an amplifier output circuit wherein the consumption current does not change, by preventing the signal-correlated current from flowing into the power source circuit.
According to the present invention, an output circuit of an amplifier comprises a three-terminal amplifier element having an input terminal, an output terminal (collector, drain), and a common terminal (emitter, source), and a constant current circuit connected to said common terminal and supplying approximately a constant current to said three-terminal amplifier element, characterized in that said output terminal is grounded, and an amplified output is taken out from between a connection point of the common terminal with the constant current circuit, and the ground. As the consumption current of the amplifier output circuit according to the present invention is solely the current flowing in the constant current circuit, there is no change in the consumption current in correlation with the output current. The amplifier output circuit according to the present invention is a constant consumption current output circuit (CCC output circuit).
The present invention has fulfilled the aim of keeping the consumption current constant while using the least number of components.
A transistor Q (three-terminal amplifier element) comprises a base B (input terminal), a collector C (output terminal) and an emitter E (common terminal). A constant current circuit CS is connected with emitter E of transistor Q. This connection point P is further connected with an amplifier output terminal 10a. Collector C is grounded.
The signal of a signal source SIG is amplified through transistor Q. The amplified signal appears between amplifier output terminals 10a and 10b. Amplifier output terminal 10b is grounded. A condenser C2 for cutting off direct current may be provided between connection point P and amplifier output terminal 10a.
Condenser C1 cuts off the direct current of signal source SIG. Resistance R1 and R2 form a bias circuit.
In Embodiment 1, the constant current circuit CS is connected with emitter E of transistor Q, so that the consumption current of transistor Q remains unchanged. By applying Embodiment 1 to audio preamplifiers, etc., it is possible to form an output portion that does not allow signal-correlated current to flow into the power source circuit.
Furthermore, in a preliminary amplifying portion (not illustrated), it is possible to similarly connect the constant current circuit S with the emitter of the transistor, thereby selecting a circuit wherein the signal causes no change in the consumption current. As result, such amplifying portion and such output portion as a whole can form a preamplifier, etc., wherein signal-correlated current does not flow into the power source circuit.
Transistors Q2 and Q3 are Darlington transistors. Constant current circuit DS is connected with the emitter of the subsequent transistor Q3. The connection point P is connected with amplifier output terminal 10a. Amplifier output terminals 10a and 10b are connected to a speaker SP.
By connecting the output transistors in Darlington connection, etc., it is possible to gain a large output current, thereby forming an output portion of an audio power amplifier, wherein signal-correlated current does not flow into the power source circuit.
Furthermore, in a preliminary amplifying portion (not illustrated), it is possible to similarly connect the constant current circuit S with the emitter of the transistor, thereby selecting a circuit wherein the signal causes no change in the consumption current. As result, such amplifying portion and such output portion as a whole can form a power amplifier, etc., wherein signal-correlated current does not flow into the power source circuit.
Embodiment 3 is an application of Embodiment 2 to a complementary output circuit. The complementary circuit comprises PNP (first polarization) transistors Q2 and Q3, and NPN (second polarization) transistors Q2′ and Q3′.
In the complementary output circuit, transistors Q2 and Q3, and transistors Q2′ and Q3′ are in Darlington connection. Constant current circuits CS and CS' are connected with the emitter of the subsequent transistors Q3 and Q3′. The amplifier output terminal 10a is connected with the connection points P and P′.
The current amplification factor of the transmitter has current dependency, which causes a distortion in the output signal. By combining PNP and NPN output transistors to form the complementary output circuit, it is possible to cancel the curvature property of the current dependency, thereby gaining an output signal with less distortion. The complementary output circuit can be structured so that signal-correlated current does not flow into the power source circuit.
In
The current supplied by the power source is solely the current defined by the constant current circuit, so the consumption current does not change according to the sound output, and the power source circuit does not affect the sound quality.
According to an embodiment of the present invention, it can be said that the reaction of the sound output flowing on the load is cancelled by the constant current source, thereby preventing the current correlated to the sound signal from flowing into the power source circuit.
According to an embodiment of the present invention, it is possible to prevent the power source circuit from affecting sound quality, as current correlated to the sound signal does not flow into the power source circuit. As result, sound can be achieved that has higher quality than ever before. Also, it is possible to prevent the sound output from affecting the power supply line.
According to an embodiment of the present invention, the consumption current is constant regardless of the size of the input signal, so when there is no or little input signal, the current is large, in other words, the idling current is large. This is especially notable in the case of power amplifiers.
When the maximum output current is +/−1 (A), the idling current need only be 0 (A) in the case of an output circuit of a Class B complementary emitter follower amplifier, and the idling current need only be 1 (A) in the case of an output circuit of a Class A complementary emitter follower amplifier. However, in the output circuit of an amplifier according to the embodiment of the present invention, the idling current becomes twice the current of 1 (A), requiring twice the idling current of that of the output circuit of a Class A complementary emitter follower amplifier.
The circuit in Non-Patent Document 2 is a source grounded circuit, which is different from the drain grounded circuit or the collector grounded circuit according to an embodiment of the present invention.
The circuit in Non-Patent Document 3 is a conventional complementary common drain (source follower), which is completely different from the circuit according to an embodiment of the present invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/055105 | 2/22/2016 | WO | 00 |
