A programmable amplifier circuit includes an amplifier, an input capacitor coupled to an input of the amplifier, a feedback capacitor coupled to the input of the amplifier and an output of the amplifier, and a switched-capacitor resistor circuit. The switched-capacitor resistor circuit is coupled between the input of the amplifier and the output of the amplifier, and configured for simulating a feedback resistor element to provide a resistance for a feedback path of the amplifier by using at least one capacitor placed between the input of the amplifier and the output of the amplifier to avoid leakage current(s) flowing back to an input of the amplifier.

A low capacitance n-channel analog switch circuit, a p-channel analog switch circuit, and a full CMOS transmission gate (T-gate) circuit are described. Resistive decoupling can be used to isolate the switch or T-gate from AC grounds, such as one or more switch control signal inputs or supply voltages. A semiconductor region that is separated from a body region of a pass field-effect transistor (FET) can be coupled to or driven to a voltage similar to the input voltage or other desired voltage to help reduce parasitic capacitance of the switch or T-gate. The switch or T-gate can have improved frequency bandwidth or frequency response. The switch can be useful in a programmable gain amplifier (PGA) or programmable gain instrumentation amplifier (PGIA) or other circuit in which excessive switch capacitance could degrade circuit performance.

A wide range differential current switching circuit can operate across a wide range of input currents and across a broad range of frequencies. A first differential current source can include a first transistor and a second transistor. The first transistor receives a switching signal and provides an output current and at output node. The second transistor receives an inverted switching signal, the first transistor and the second transistor coupled to each other at a tail node. A current source provides an input current to the tail node. A third transistor can provide a boost current to the tail node while the first transistor is off.

The present invention provides a burst mode trans-impedance amplifier, comprising: a voltage input circuit, used for sensing an optical signal and converting the optical signal into an input voltage signal; a differential circuit, having two input ends and an output end, wherein one input end is coupled to the voltage input circuit and is used for receiving the input voltage signal, the other input end is coupled to a threshold voltage signal, and the output end is used for regulating and outputting a differential voltage signal according to the input voltage signal and the threshold voltage signal; and a feedback regulation circuit, having an input end and an output end, wherein the input end is coupled to the output end of the differential circuit and is used for receiving the differential voltage signal, and the output end is coupled to the voltage input circuit.

A wide range differential current switching circuit can operate across a wide range of input currents and across a broad range of frequencies. A first differential current source can include a first transistor and a second transistor. The first transistor receives a switching signal and provides an output current and at output node. The second transistor receives an inverted switching signal, the first transistor and the second transistor coupled to each other at a tail node. A current source provides an input current to the tail node. A third transistor can provide a boost current to the tail node while the first transistor is off.

An integrated circuit amplifier configurable to be either a programmable gain amplifier or an operational amplifier comprises two output blocks, one output block is optimized for programmable gain amplifier operation, and the other output block is optimized for operational amplifier applications. A common single input stage, input offset calibration and bias generation circuits are used with either amplifier configuration. Thus duplication of the input stage, offset calibration and bias generation circuits are eliminated while still selectably providing for either a programmable gain amplifier or operational amplifier configuration.

Systems, methods and apparatus for efficient power control of an RF amplifier for amplification of a constant envelope RF signal are described. A reduction in a size of a pass device of an LDO regulator is obtained by removing the pass device of the LDO regulator from a main current conduction path of the RF amplifier. Power control is provided by varying one or more gate voltages to cascoded transistors of a transistor stack of the RF amplifier according to a power control voltage. Various configurations for controlling the gate voltages are presented by way of a smaller size LDO regulator or by completely removing the LDO regulator. In a case where a supply voltage to the transistor stack varies, such as in a case of a battery, a compensation circuit is used to adjust the power control voltage in view of a variation of the supply voltage, and therefore null a corresponding drift in output power of the RF amplifier.

Apparatus and methods for envelope tracking systems with automatic mode selection are provided herein. In certain configurations, a power amplifier system includes a power amplifier configured to provide amplification to a radio frequency signal and to receive power from a power amplifier supply voltage, and an envelope tracker including a signal bandwidth detection circuit configured to generate a detected bandwidth signal based on processing an envelope signal corresponding to an envelope of the radio frequency signal. The envelope tracker further includes a switch bank configured to receive a plurality of regulated voltages, a filter configured to filter an output of the switch bank to generate the power amplifier supply voltage, and a mode control circuit configured to control a filtering characteristic of the filter based on the detected bandwidth signal.

A contactless communication device includes a receiver unit having differential input terminals for connecting to an antenna. The receiver unit is coupled to a transmitting device and receives an RF signal transmitted by the transmitting device. A first comparator is adapted to generate a first comparator output signal indicative of a relationship between a voltage at a positive input terminal of the receiver unit and a first reference voltage. A second comparator is adapted to generate a second comparator output signal indicative of a relationship between a voltage at a negative input terminal of the receiver unit and a second reference voltage. A first voltage regulation circuit is adapted to regulate the voltage at the positive input terminal in response to the first comparator output signal. A second voltage regulation circuit is adapted to regulate the voltage at the negative input terminal in response to the second comparator output signal.

An apparatus includes a radio-frequency (RF) receiver. The RF receiver includes a single-balanced passive mixer driven by the output of a low noise amplifier (LNA) and a passive filter driven by an output of the single-balanced passive mixer. The RF receiver further includes a programmable gain amplifier (PGA) having an input resistance that generates noise, where the PGA is driven by an output of the passive filter, and the noise generated by the input resistance of the PGA is suppressed.