Amplifier for stably maintaining a constant output

An amplifier comprising:

• a plurality of basic amplifiers connected in cascade, each of said basic amplifiers comprising:
• a limiting amplifier, including a signal input terminal and a reference voltage input terminal, for amplifying an input signal applied to the signal input terminal and for producing a limited output signal when an amplitude of the input signal is greater than a predetermined value, and a level of the input signal is within a predetermined range with regard to a reference voltage applied to the reference voltage input terminal;
• and
• an automatic threshold control circuit for supplying the reference voltage input terminal of said limiting amplifier with a substantially middle value between a top value of the input signal and a bottom value of the input signal as the reference voltage.

A limiting amplifier for amplifying an input signal and for producing a limited output signal having a limited amplitude, said limiting amplifier comprising:

• a first amplifier including a first amplifying stage and a first output stage, said first amplifying stage and said first output stage including transistors of a first conductivity type;
• and
• a second amplifier, including a second amplifying stage and a second output stage, connected in cascade to said first amplifier, said second amplifying stage and said second output stage including transistors of a second conductivity type;
• wherein said second amplifier is a non-inverting amplifier, and one of upper and lower limits of the limited output signal is limited by said first output stage, and the other of the upper and lower limits of the limited output signal is limited by said second output stage.

A limiting amplifier for amplifying an input signal and for producing a limited output signal having a limited amplitude, said limiting amplifier comprising:

• a first amplifier including a first amplifying stage and a first output stage, said first amplifying stage and said first output stage including transistors of a first conductivity type;
• and
• a second amplifier, including a second amplifying stage and a second output stage, connected in cascade to said first amplifier, said second amplifying stage and said second output stage including transistors of a second conductivity type;
• wherein said second amplifier is an inverting amplifier including a signal input terminal and a reference voltage input terminal, and one of upper and lower limits of the limited output signal is limited by biasing a reference voltage applied to said reference voltage input terminal from a center of a linear operating region of said second amplifier, and the other of the upper and lower limits of the limited output signal is limited by said second output stage.

An amplifier comprising:

• a limiting amplifier, including a signal input terminal and a reference voltage input terminal, for amplifying an input signal applied to the signal input terminal and for producing a limited output signal when an amplitude of the input signal is greater than a predetermined value, and a level of the input signal is within a predetermined range with regard to a reference voltage applied to the reference voltage input terminal;
• and
• an automatic threshold control circuit for supplying the reference voltage to the reference voltage input terminal of said limiting amplifier,
• wherein said automatic threshold control circuit comprises a top-hold circuit for detecting and holding a top value of the input signal, and a voltage divider for producing, as the reference voltage, a divided voltage between the output of said top-hold circuit and a fixed voltage externally supplied from a fixed voltage source, and
• wherein voltages of the input terminal and output terminal of said top-hold circuit become substantially equal when the top-hold circuit is reset by an external reset signal and wherein said fixed voltage is set at a value lower than the voltage at said signal input terminal during a signal-less state so as to assure the output of said limiting amplifier is at a low value during said signal-less state.

An amplifier comprising:

• a limiting amplifier, including a signal input terminal and a reference voltage input terminal, for amplifying an input signal applied to the signal input terminal and for producing a limited output signal when an amplitude of the input signal is greater than a predetermined value, and a level of the input signal is within a predetermined range with regard to a reference voltage applied to the reference voltage input terminal;
• and
• an automatic threshold control circuit for supplying the reference voltage to the reference voltage input terminal of said limiting amplifier,
• wherein said automatic threshold control circuit comprises a bottom-hold circuit for detecting and holding a bottom value of the input signal, and a voltage divider for producing, as the reference voltage, a divided voltages between the output of said bottom-hold circuit and a fixed voltage externally supplied, and
• wherein voltages of the input terminal and output terminal of said bottom-hold circuit become substantially equal when the bottom-hold circuit is reset by an external reset signal.