Abstract: In accordance with an embodiment, method for generating an output signal of an amplifier having an increased signal to noise ratio includes receiving a first signal at an input terminal of the amplifier that is not part of a differential input. The input terminal of the amplifier is a sole input terminal of the amplifier. The first signal has an externally received portion and a feedback portion. A first amplified signal is generated at an output of the amplifier. High frequency components of the first amplified signal may be filtered. A feedback signal is generated at the sole input terminal of the amplifier in response to the first output signal.

Abstract: In accordance with an embodiment, method for generating an output signal of an amplifier having an increased signal to noise ratio includes receiving a first signal at an input terminal of the amplifier that is not part of a differential input. The input terminal of the amplifier is a sole input terminal of the amplifier. The first signal has an externally received portion and a feedback portion. A first amplified signal is generated at an output of the amplifier. High frequency components of the first amplified signal may be filtered. A feedback signal is generated at the sole input terminal of the amplifier in response to the first output signal.

Abstract: In accordance with an embodiment, an amplification circuit includes an amplifier connected to a filter, wherein the amplifier has an input and an output and the filter has an input connected to the output of the amplifier. The amplification circuit includes a comparator that has an input connected to the output of the filter and an input coupled for receiving a reference voltage. The output of the comparator is connected to the input of the amplification circuit. In accordance with another embodiment, a method for generating an output signal is provided that includes generating an amplified signal by amplifying a signal that has an input portion and a feedback portion. A comparison signal is generated in response to comparing the signal with a reference signal and the comparison signal is used to set the output voltage to be substantially equal to the reference voltage.

Abstract: In accordance with an embodiment, an amplification circuit includes an amplifier connected to a filter, wherein the amplifier has an input and an output and the filter has an input connected to the output of the amplifier. The amplification circuit includes a comparator that has an input connected to the output of the filter and an input coupled for receiving a reference voltage. The output of the comparator is connected to the input of the amplification circuit. In accordance with another embodiment, a method for generating an output signal is provided that includes generating an amplified signal by amplifying a signal that has an input portion and a feedback portion. A comparison signal is generated in response to comparing the signal with a reference signal and the comparison signal is used to set the output voltage to be substantially equal to the reference voltage.

Abstract: This invention provides a voltage controlled variable gain amplifier circuit that varies its gain linearly and continuously against a gain control voltage VC. The voltage controlled variable gain amplifier circuit includes a first differential amplifier, a second differential amplifier, a gain control voltage/current conversion circuit and a reference current generation circuit. The first differential amplifier and the second differential amplifier are connected in series. The gain control voltage/current conversion circuit converts the gain control voltage VC into a gain control current IC that varies linearly against the gain control voltage VC. Drain currents Id1 and Id2 of first and second differential input transistors vary linearly against the gain control current IC.

Abstract: The invention provides an amplifier circuit of a capacitor microphone of which the noise resistance against noise of a supply voltage is enhanced. In an amplifier circuit of a capacitor microphone of the invention, while a noise component of a supply voltage is applied to one inversion input terminal of an operational amplifier of an amplification portion through a parasitic capacitor existing between an external power supply wiring and an external wiring that are adjacent to each other, the problem noise component of the supply voltage is applied to the other non-inversion input terminal by capacitive coupling to an internal power supply wiring. Therefore, the noise component is cancelled at the operational amplifier.

Abstract: This invention provides a voltage controlled variable gain amplifier circuit that varies its gain linearly and continuously against a gain control voltage VC. The voltage controlled variable gain amplifier circuit includes a first differential amplifier, a second differential amplifier, a gain control voltage/current conversion circuit and a reference current generation circuit. The first differential amplifier and the second differential amplifier are connected in series. The gain control voltage/current conversion circuit converts the gain control voltage VC into a gain control current IC that varies linearly against the gain control voltage VC. Drain currents Id1 and Id2 of first and second differential input transistors vary linearly against the gain control current IC.

Abstract: The invention provides an amplifier circuit of a capacitor microphone of which the noise resistance against noise of a supply voltage is enhanced. In an amplifier circuit of a capacitor microphone of the invention, while a noise component of a supply voltage is applied to one inversion input terminal of an operational amplifier of an amplification portion through a parasitic capacitor existing between an external power supply wiring and an external wiring that are adjacent to each other, the problem noise component of the supply voltage is applied to the other non-inversion input terminal by capacitive coupling to an internal power supply wiring. Therefore, the noise component is cancelled at the operational amplifier.

Abstract: In some preferred embodiments, a switched capacitor circuit configured to change its equivalent resistance depending on the frequency of an input clock signal and a resistor element are connected in series. A power source voltage is divided by the equivalent resistance of the switched capacitor circuit and the resistance of the resistor element, and the divided voltage is inputted to a Schmitt circuit. The Schmitt circuit outputs a high-level signal when the inputted divided voltage is higher than a threshold voltage and a low-level signal when the inputted divided voltage is lower than a threshold voltage. Thus, depending on the frequency of the input clock signal, a high-level signal or a low-level signal is outputted.