Crystal Semiconductor Corporation

Baker P Scott, Iii

Larry L Harris

Mohammad J Navabi

Adrian B Early

Eric J Swanson

Stephen F Bily

An amplifier having an inverting and a non-inverting input and at least one output is compensated by dynamically varying the transconductance of a gain stage in accordance with the gain of the output stage of the amplifier. The amplifier comprises a gain section having at least one output, where a gm of the gain section varies with a transconductance control signal. The amplifier further comprises an output stage comprising a output drive device controlled by an output of the gain section. A bias control circuit is coupled to drive the transconductance control input of the gain section, the bias control circuit increasing a differential mode transconductance of the first gain stage when the active pullup or pulldown output drive device has low gain.

Amplifier having frequency compensation by gain degeneration

An amplifier with controlled output impedance utilizing current and voltage feedback to set gain and output impedance is disclosed. The voltage feedback is provided by feedback resistor connected from the output to the inverting input. The current feedback is provided by feeding a current proportional to the output current directly to the inverting input of the amplifier. An error amplifier is used to maintain the proper ratio of the current feedback to the output current and to cancel the effects of the output device impedance on the overall output impedance. Two such amplifiers driven by complimentary signals form a differential amplifier with controlled output impedance. Because the output impedance is a function of the voltage feedback resistance and the current feedback ratio, it is possible to digitally control the output impedance by changing the feedback resistance and/or the current feedback ratio.

Controlled impedance amplifier

An integrated circuit apparatus and method is provided for utilizing voltage dividers and differential amplifiers. An apparatus and method for dividing a voltage with a resistor voltage divider and for employing the voltage divider in an integrated circuit. The resistor voltage divider utilizes inaccessible compensation taps that are placed between nonlinearly spaced output taps. The compensation taps reduce the impact of tap resistance on the voltage divider transfer function. The number of inaccessible compensation taps placed between output taps is dependant upon a chosen tap density that is substantially maintained across the body of the resistor voltage divider. The resistor may be used in integrated circuits employing amplifiers, such as volume control circuitry. A differential amplifier is provided with an input common mode feedback loop that compensates for signal distortion due to a common mode signal. The effects that mode changes in the input transistors have on the differential gain are minimized by the input common mode feedback loop. The differential signal path has only one low frequency mode. The amplifier includes circuitry that acts on the input differential signal and circuitry that acts on the varying input common mode voltage. The common mode feedback is achieved using a variable current sink transistor. The gate voltage of the variable current sink transistor is controlled by the sum of currents flowing through transistors that are connected to the drains of the differential input transistors.

Amplifier with input common mode compensation

An apparatus and method is provided for dividing a voltage with a resistor voltage divider and for employing the voltage divider in an integrated circuit. The resistor voltage divider utilizes inaccessible compensation taps that are placed between nonlinearly spaced output taps. The compensation taps reduce the impact of tap resistance on the voltage divider transfer function. The number of inaccessible compensation taps placed between output taps is dependant upon a chosen tap density that is substantially maintained across the body of the resistor voltage divider. The resistor may be used in integrated circuits employing amplifiers, such as volume control circuitry.

Integrated voltage divider and circuit employing an integrated voltage

A semiconductor capacitor for use in an analog-to-digital converter includes two parallel connected capacitors with separate lower plates (44) and (46) fabricated of polycrystalline silicon and upper plates (52) and (54) also fabricated of polysilicon. The plates are separated by capacitive oxide dielectric structures (48) and (50). They are interconnected such that the lower plate (44) of one capacitor is connected to the upper plate (54) of the other capacitor and the lower plate (46) of the other capacitor is connected to the upper plate (52) of the first capacitor. With such a configuration, the odd ordered non-linearities contributing to the voltage coefficient errors are cancelled.

Compensated capacitors for switched capacitor input of an

A switched capacitor input circuit that reduces nonlinear input current due to input switch charge injection. The addition of a shunt capacitor with a series switch to signal ground at the input switch of a sampling network is used to sample and hold the input switch charge injection. This input switch charge injection can then be returned as input switch channel charge during the next sampling phase eliminating the need for the input signal to supply this charge.

Input sampling switch charge conservation

A high speed feedback amplifier is frequency compensated utilizing circuitry that does not cause distortion in the amplifier nor does it limit the slew rate of the amplifier. In one embodiment compensation circuitry drives one side of the compensation capacitor forcing the signal voltage across the compensation capacitor to zero while still providing bandwidth compensation. Since no current gets driven into the capacitor, no distortion or slew limitations are created by the compensation. In a second embodiment the voltage across the compensation capacitor is allowed to change, however the signal current for the compensation capacitor is supplied by a linear charging circuit which removes this charging requirement from the amplifier. Therefore, as in the first embodiment, no distortion or slew limitation is created by the addition of the frequency compensation.

Slew rate enhanced linear amplifier

An amplifier with controlled output impedance has a first output connected to the inverting input of the amplifier, and a second output, which forms the output of the amplifier, connected through a feedback conductance to the inverting input of the amplifier. A input conductance is connected from the inverting input to ground, and the input signal is connected to the positive input of the amplifier. The first and second outputs are provided by first and second current output stages. The currents provided by the first and second output stages are proportional to each other by a predetermined ratio. By proper selection of this predetermined ratio and the feedback and input conductances the desired output impedance and overall gain of the amplifier into a given load can be achieved.

Amplifier with controlled output impedance

A wide bandwidth transconductance amplifier utilizing internal feedback is stabilized over a wide range of output currents. A compensation driver circuit senses the output current in the amplifier and feeds it back through a compensation capacitor. This keeps the bandwidth of the amplifier constant and optimally stabilized over a 16 to 1 range in output current. This compensation scheme eliminates compensation compromises that can limit the useful dynamic range of transconductnce amplifiers while offering a wide bandwidth low distortion transconductance with high output impedance over frequency.

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Austin, TX, United States of America

Baker P Scott, Iii