Sanyo Electric Co., Ltd.

Masanori Fujisawa

Hiroshi Kojima

Kazuhisa Ishiguro

Kenichi Kokubo

A loudness control circuit emphasizes low frequency components in audio signals. A secondary low-pass filter select low frequency components of the audio signals, inverting a phase of the audio signals. The phase-inverted signals and audio signals are respectively inputted to an inverting input terminal and non-inverting input terminal of an operational amplifier to obtain audio signals whose low frequency components are emphasized. These signals have the same phase as the phase of the inputted audio signals. The output of the low-pass filter is amplified to obtain a signal having low frequency components whose phase is inverted. Both the audio signal whose low frequency components have been amplified and the low frequency components whose phase has been inverted are applied to a speaker to reproduce sounds with their low frequency components dynamically emphasized.

Loudness control circuit

An amplifying circuit with a small current consumption which is used for a portable radio, personal stereo systems or the like. The operating current of a differential amplifier, which is the main component of the amplifying circuit, is controlled by a first current circuit, which is a fixed constant-current source, and a second current circuit, which is a variable current source. The current of the second current circuit is controlled by an input audio signal with the voltage subjected to full-wave rectification. As a result, when the amplitude of the input signal is small, only a slight operating current is consumed by the first current circuit, thereby saving electricity. On the other hand, when the amplitude of an input audio signal is large, the current of the second current circuit also increases therewith, so that the amplifier flows a sufficiently large output current. Thus, it is possible to amplify the current in correspondence with the amplitude of an input signal, while reducing the operating current when the amplitude of an input signal is small, thereby reducing the current consumption.

Amplifying circuit

The present invention provides a B class push-pull amplifying circuit suitable for use in a headphone type tape recorder and the like. The amplifying circuit utilizes a current mirror circuit system in its output transistors to provide an idling current for compensating for crossover distortion by using the mirror ratio. The current mirror circuit system includes a pair of output current mirror circuits complimentarily coupled with each other. One branch of these output current mirror circuits includes a diode-connected transistor, the emitter current path of which is ON-OFF controlled by a drive transistor in the other branch. Thus, when no signal is input, the respective one of the current mirror output circuits complimentarily coupled with each other functions as a current mirror circuit such that the small idling current determined by the mirror ratio will pass therethrough. On the other hand, the inputting of a signal causes the output of the opposite side drive transistor to make the current mirror circuit inoperative. The output transistor functions as a normal amplifying circuit. An amplification factor h.sub.FE provided at this time can reliably assure a sufficiently large amplification degree.

Push-pull power amplifying circuit

An offset voltage at one pair of differential amplifier transistors for effecting the differential amplification of an input signal is suppressed. To achieve this aim, the base current of a pair of differential amplifier transistors is supplied from a current generator circuit separately provided. This current generator circuit has a very small current flow, and is composed of another pair of differential amplifier transistors to which a reference voltage identical with the bias voltage of the first differential amplifier transistors is applied, a transistor for reference current use for delivering a current at a current density identical with the current density of the first differential amplifier transistors, a base current supply transistor for supplying power to the reference current transistor, and two current supply transistors for delivering a current identical with the current of the simulation base-current supply transistor. The transistors of the second differential amplifier act to make the base potential of the transistor for operation simulation use identical with a reference voltage, and then the simulation base current supply transistor supplies the base current to the operation simulation transistor. Thereafter, since the transistor for base current supply use delivers an identical current to the base current from the simulation base current supply transistor, the occurrence of the offset voltage in the differential amplifier transistors can be suppressed.

Amplifier circuit

An amplifier circuit includes a negative feedback connected amplifier and a series circuit comprising a capacitor, one end of which is connected to an output terminal of the amplifier, and a resistor, one end of which is connectable to a reference potential. A comparator is provided which has first and second inputs and one output. The first input is connected to a junction between the capacitor and the resistor, the second input is connected to an output of the amplifier, and the output of the comparator is connected to one input of the amplifier. The comparator does not react to an AC signal of a specific frequency band, but operates to set the output offset voltage only to one fractional part of the transition gain, and therefore operates to accomplish offset compensation without using a large capacitor.

An amplifier comprises a first amplifier circuit and a second amplifier circuit. An input signal voltage and an input DC bias voltage are applied to the first amplifier circuit, and an input DC bias voltage is applied to the second amplifier circuit. The input DC bias voltages applied to the first amplifier circuit and the second amplifier circuit are common to each other. Output bias voltages of the first amplifier circuit and the second amplifier circuit become equal to each other. The amplified signal voltages are applied to a load connected between outputs of the amplifier circuits.

Growing community of inventors

Kumagaya, Japan

Masanori Fujisawa