Abstract: Apparatus (301) for switchable attenuation of a differential input signal from a microphone includes positive and negative non-attenuating paths (406, 410) have n- and p-type MOSFETs (421, 422, 423, 424) in back-to-back configurations; positive and negative attenuating paths (405, 409) have n- and p-type MOSFETs (415, 416, 418, 419) in back-to-back configurations in combination with resistors; a gate driver (425) applies a drive signal of one polarity (QNEG) to gates of the n-type MOSFETs in the attenuating paths and the p-type MOSFETs in the non-attenuating paths, and a drive signal of opposite polarity (QPOS) to the gates of the p-type MOSFETs in the attenuating paths and the n-type MOSFETs in the non-attenuating paths; and the state of the MOSFETs depends on the drive signals at their gates, and thus the input signal may be routed via either the non-attenuating paths or the attenuating paths by controlling the drive signals.

Abstract: Apparatus (301) for switchable attenuation of a differential input signal from a microphone includes positive and negative non-attenuating paths (406, 410) have n- and p-type MOSFETs (421, 422, 423, 424) in back-to-back configurations; positive and negative attenuating paths (405, 409) have n- and p-type MOSFETs (415, 416, 418, 419) in back-to-back configurations in combination with resistors; a gate driver (425) applies a drive signal of one polarity (QNEG) to gates of the n-type MOSFETs in the attenuating paths and the p-type MOSFETs in the non-attenuating paths, and a drive signal of opposite polarity (QPOS) to the gates of the p-type MOSFETs in the attenuating paths and the n-type MOSFETs in the non-attenuating paths; and the state of the MOSFETs depends on the drive signals at their gates, and thus the input signal may be routed via either the non-attenuating paths or the attenuating paths by controlling the drive signals.

Abstract: An amplifier for amplifying a differential audio signal, having common-mode rejection and digital gain control, includes a current source (401) which supplies a constant level of current to a first current path (I1) and a second current path (I2), and input stage (403) which modulates the current in the current paths in response to a differential input signal, and an output stage (405) which produces an output signal by amplifying the difference in current between the current paths, a degree of feedback provided to the input stage by a feedback stage (402) that modulates the current in the current paths in response to the output signal, and the degree of modulation by the feedback stage is determined by the attenuation provided by at least one multiplying digital-to-analog converter (407) located therein.

Abstract: An equalizer (402) is shown, having a state variable filter in which a first MDAC (502) is coupled to a first integrator (503) and a second MDAC (504) is coupled to a second integrator (505) to allow control of the corner frequency of the state variable filter. The MDACs are each configured to provide variable attenuation in a plurality of discrete steps. A digital attenuation controller is coupled to and adjusts the attenuation of the MDACs independently, and effects a one-step increase in the corner frequency of the state variable filter by first determining the attenuation levels of the MDACs, and then controlling the attenuation levels of the MDACs in accordance with their existing attenuation levels.

Abstract: An equalizer (402) is shown, having a state variable filter in which a first MDAC (502) is coupled to a first integrator (503) and a second MDAC (504) is coupled to a second integrator (505) to allow control of the corner frequency of the state variable filter. The MDACs are each configured to provide variable attenuation in a plurality of discrete steps. A digital attenuation controller is coupled to and adjusts the attenuation of the MDACs independently, and effects a one-step increase in the corner frequency of the state variable filter by first determining the attenuation levels of the MDACs, and then controlling the attenuation levels of the MDACs in accordance with their existing attenuation levels.

Abstract: An amplifier for amplifying a differential audio signal, having common-mode rejection and digital gain control, includes a current source (401) which supplies a constant level of current to a first current path (I1) and a second current path (I2), and input stage (403) which modulates the current in the current paths in response to a differential input signal, and an output stage (405) which produces an output signal by amplifying the difference in current between the current paths, a degree of feedback provided to the input stage by a feedback stage (402) that modulates the current in the current paths in response to the output signal, and the degree of modulation by the feedback stage is determined by the attenuation provided by at least one multiplying digital-to-analog converter (407) located therein.

Abstract: A method of amplifying an output signal from a microphone or audio transducer so as to introduce a controllable degree of distortion for inputs having a wide dynamic range, comprising the steps of: receiving a differential input signal from a microphone or audio transducer, applying said differential signal to a differential amplifier, said differential amplifier having a negative feedback path to control the gain of said amplifier; and providing non-linear circuitry in said feedback path so as to introduce distortion, such that the degree of distortion present is related to the level of the output signal and not to the level of the input signal.

Abstract: A differential audio amplification apparatus with common mode rejection is shown, having a first input current path (401) and a second input current path (402) with a shunting input resistance (400) therebetween. The apparatus also has a first output current path (403) and a second output current path (404) with a shunting output resistance (405) therebetween. Differential amplifiers (412, 413) are provided with feedback connecting the input paths with the output paths and providing an output signal. The output shunting resistance (405) is controlled to provide gain control while maintaining common mode rejection.

Abstract: A differential audio amplification apparatus with common mode rejection is shown, having a first input current path (401) and a second input current path (402) with a shunting input resistance (400) therebetween. The apparatus also has a first output current path (403) and a second output current path (404) with a shunting output resistance (405) therebetween. Differential amplifiers (412, 413) are provided with feedback connecting the input paths with the output paths and providing an output signal. The output shunting resistance (405) is controlled to provide gain control while maintaining common mode rejection.

Abstract: A method of amplifying an output signal from a microphone or audio transducer so as to introduce a controllable degree of distortion for inputs having a wide dynamic range, comprising the steps of: receiving a differential input signal from a microphone or audio transducer, applying said differential signal to a differential amplifier, said differential amplifier having a negative feedback path to control the gain of said amplifier; and providing non-linear circuitry in said feedback path so as to introduce distortion, such that the degree of distortion present is related to the level of the output signal and not to the level of the input signal.