JPH0335847B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention is characterized in that, in a speaker amplifier comprising a negative feedback amplifier, the ratio of feedback resistance to input resistance, which determines the amplification rate, is made variable by an external control signal. This invention relates to an envelope sound generation circuit.

An object of the present invention is to enable the simplest and most efficient control of the attenuation amplitude of a single note.

Another object of the present invention is to create a C
-The goal is to realize a MOS driver.

Still another object of the present invention is to realize a C-MOS driver that directly drives a piezoelectric speaker and creates envelope sound.

Conventional loudspeaker sound pressure controllable amplifiers are generally push-pull amplifiers using bipolar transistors. Therefore, it is extremely difficult to set conditions for bias setting, and the addition of a capacitive element is unavoidable. Furthermore, in electronic devices that require low power consumption, it is becoming more difficult to employ a current control method using bipolar transistors. However, in order to reduce power consumption, an example of an envelope sound generation circuit made of C-MOS uses pulse width control to control the sound pressure since amplitude control is difficult. This method has drawbacks such as sound distortion due to harmonic components and the impossibility of push-pull drive.

The present invention improves the above-mentioned drawbacks, changes the swing width in a stepwise manner by digital control, and furthermore,
This relates to an amplifier that enables push-pull drive, and because it can be made with C-MOSIC, it is suitable for small devices such as watches and calculators, and can also be made directly with C-MOSC.
It is a MOSIC device that can push-pull drive high impedance speakers such as piezoelectric speakers. Furthermore, since the circuit configuration is extremely simple, it is possible to reduce costs, and to provide a highly reliable circuit with little variation in output.

A diagram of the principle of the present invention is shown in FIG. 1 and 3 in the figure are P-channel MOS transistors, 2,
4 is an N-channel MOS transistor; 5,
6, 7, and 8 are resistive elements, and 9 is a piezoelectric speaker. From input 10, resistors 6 and 6 are connected between the sources and gates of P-channel transistors 1 and 3, respectively.
7 is connected. and gate and input 10,
Resistors 5 and 8 are connected between the terminals 11 and 11, respectively. A pair of terminals of the speaker 9 are each connected to a connection point between the drains of two sets of P-channel transistors and N-channel transistors. A drive signal is input, and its inverted signal (180° phase shift difference) is input from input 11. In the figure, 5, 6, 1 and 8, 7, 3 represent resistance 6/resistance 5 and resistance 7/resistance, respectively.
This is an amplifier determined by resistor 8, and when the amplifier composed of 5, 6, and 1 operates, transistor 2
is OFF, transistor 4 is ON, and when the amplifier composed of 8, 7, and 3 is operated, transistor 4 is OFF and transistor 2 is ON. Therefore, a pulse train of any frequency from input 10, input 11
When the inverted pulse train is inputted to each of the speakers 9, the speaker 9 is push-pull driven and vibrates with a potential difference twice the input voltage. At this time, if the resistors 5 and 8 are changed at a cycle longer than the pulse train, the amplification rate will change, and the amplitude of the speaker will change accordingly.

FIG. 2 depicts the waveform diagram. 1
2 and 13 are the input signal waveforms 10 and 11 in Figure 1, 14 is the voltage waveform across the speaker, and 15 is the voltage across the speaker when the resistance values of resistors 5 and 8 in Figure 1 are successively increased. This is the voltage waveform of

FIG. 3 shows an example of a circuit for actually changing the resistance described above, in which 18, 19, and 20 are drain transmission gates, and 24, 25, and 26 are 18 and 26, respectively.
19, 20 control signals, 21, 22, 2
3 are resistors having resistance values of x, 2x, and 4x (x is an arbitrary value), respectively. Reference numeral 16 represents an input of a drive signal, and reference numeral 17 represents an output. Both ends of 16 and 17 correspond to the resistors 5 and 8 shown in FIG. 24 is "1"
When it becomes "18", it turns ON, and when it becomes "0", it turns OFF.
do. The same applies to 19 and 20. Therefore, 26,
25, 24 are each 100; 010; 110; 001; 101;
011; At the time of 111, the resistance values at both ends of 16 and 17 are respectively
4x; 2x; 4/3x; x; 4/5x; 2/3x; 4/7x.

FIG. 29 shows the relationship between the control signal at this time, the resistance value at both ends of 16 and 17, and the voltage waveform at both ends of the speaker. 29 shows the case where the control signals of the transmission gates 18, 19, and 20 are changed at the same timing as the frequency of the input signal. By changing the change timing of the control signal with respect to the frequency of the input signal, it is possible to obtain a decaying sound similar to the ringing of a bell or an attack sound with a sharp tone. In this embodiment, the control signal is 3 bits, but by increasing the number of bits, the variable range can be increased and a smooth envelope waveform with higher resolution can be obtained.

As explained above, according to the present invention, the envelope of the output sound can be digitally controlled by control signals of multiple gates, so various sounds such as attack sounds and decay sounds can be easily created quickly and accurately. be able to.

Furthermore, envelope control, that is, timbre control, is possible with a simple configuration that involves adding a plurality of resistors and a plurality of switches controlled by control signals to a normal push-pull drive circuit.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the principle of the present invention. 1, 3...P channel MOS transistor,
2, 4...N-channel MOS transistor, 5,
8...variable resistor, 6,7...resistance, 10,11...
Input, 27...Power, 28...GND. FIG. 2 is an example of the signal waveform in FIG. 1. 12...Waveform of input 10 in FIG. 1, 13
...The waveform of the input 11 in FIG. 1, 14...The voltage waveform at both ends of the speaker 9 in FIG. 1, 1
5... Voltage waveform across the speaker 9 when the resistors 5 and 8 in FIG. 1 are varied; 29... Voltage waveform across the speaker 9 due to the variable resistor in FIG. 3. FIG. 3 is an example of the variable resistor in FIG. 1. 16...Input, 17...Output, 18,19,2
0...transmission gate, 24, 25,
26...18, 19, 20 control signals,
21, 22, 23...Resistance.

Claims (1)

[Claims] 1. Two sets of transistor connections in which the drains of a P-channel transistor and an N-channel transistor are connected to each other, and a pair of terminals each connected to the drain connection points of the two sets of transistor connections. In a speaker drive circuit for push-pull driving a speaker, the P channel transistor or the N
At least one of the channel transistors has a feedback resistor connected between the source and the gate, and an input resistor connected between the gate and the input section of the speaker drive circuit, and the feedback resistor or the input resistor is The plurality of bits of the control signal are comprised of a plurality of switch means selectively controlled by a plurality of bits of control signal and a plurality of resistors connected to the plurality of switch means, and the plurality of bits of the control signal change according to a drive signal inputted to the input section. A speaker drive circuit characterized in that envelope control is performed by selectively opening and closing the plurality of switch means to change the drive output to the speaker.