A transistor cell can be modeled as a transistor with a collector, a base, and an emitter operating with a current at the collector to produce a minimum transconductance in the transistor cell that increases a current gain and improves at least one operating characteristic of the transistor cell. The operating characteristics include bandwidth, gain, and output power.

The inventive concepts relate to variable gain amplifiers. The variable gain amplifier including an amplifier, a first fixed resistor and a first variable resistor, a second fixed resistor and a second variable resistor, a third fixed resistor and a third variable resistor, a fourth fixed resistor and a fourth variable resistor, a first output terminal and a second output terminal, and a decoder may be provided. The decoder is configured to receive first control bits, generate second control bits from the first control bits, generate third and fourth control bits from the first or second control bits, respectively, transmit the first control bits and the third control bits to the third and fourth variable resistors to adjust resistance values, and transmit the second and fourth control bits to first and second variable resistors to adjust resistance values.

Systems and methods for switching on and off a power amplifier including a signal input receiving an input signal and a signal output providing an output signal. The power amplifier includes a control input receiving a gain control signal indicating a requested gain and a control input receiving a mute control signal indicating whether the signal output should be switched on or switched off. A control unit determines whether the signal output of the power amplifier should be switched on and/or off, and if switched on receives data identifying a switch-on ramp and if switched off receives data identifying a switch-off ramp. The control unit generates the mute control signal to switch on the signal output of the power amplifier on or off, and generates the gain control signal as a function of the data identifying the switch-on or switch-off ramp to thereby increase or decrease the gain control signal.

A variable gain amplifier includes an input transistor, an auxiliary transistor, an active inductor and an input current replica circuit. The input transistor is arranged for receiving an input signal to generate an output signal at an output terminal. The auxiliary transistor is coupled to the output terminal of the input transistor, wherein a current of the output terminal flows into the input transistor and the auxiliary transistor. The active inductor is coupled to the output terminal of the input transistor. The input current replica circuit is coupled to the output terminal of the input transistor, wherein a current flowing through a portion of the input current replica circuit is equal to the current flowing through the input transistor, and both a current of the active inductor and the current of the portion of the input current replica circuit flow into the output terminal of the input transistor.

A driver that drives an optical device, such as laser diode (LD) and/or optical modulator, is disclosed. The driver includes a variable gain amplifier (VGA) and a post amplifier. The post amplifier amplifies an output of the VGA to a preset amplifier as varying the gain of the VGA. The VGA includes two differential pairs each amplify the input signal oppositely in phases thereof and outputs of the differential pairs are compositely provided to the post amplifier. The gain of the VGA is varied by adjusting contribution of the second differential pair to the output of the VGA.

A variable gain amplifier having stabilized frequency response for widened gain control range. A resistor-capacitor compensation network is provided between two differential current input ports and corresponding emitter nodes of cross-coupled four transistors in the variable gain amplifier to desensitize the gain control voltages to the system noise and provide compensation to the VGA frequency response when the differential gain control voltage varies the gain setting, yielding a substantially stabilized frequency response over a 3 dB bandwidth ranging from 1 GHz to 60 GHz with a widened gain control range up to 12 dB without increasing power consumption.

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.

At least some embodiments are directed to a system comprising an amplifier containing a first bias current source and configured to provide an output voltage at a node, a gain stage coupled to the node and comprising a second bias current source, and a buffer stage coupled to the node and comprising third and fourth bias current sources and an additional set of bias current sources, the third and fourth bias current sources are able to activate output transistors that are configured to increase current provided to a load. The system also comprises a controller configured to activate the first bias current source, to activate the second bias current source after the first bias current source is activated, to activate the bias current sources in the set after the first bias current source is activated, and to activate the third and fourth bias current sources after the first and second bias current sources are activated and after the bias current sources in the set are activated.

Use of a closed loop APC may involve a problem of cost and power consumption due to increased circuit scale.

The semiconductor device includes a power amplifier that amplifies an output from a transmission circuit and a regulator that supplies power to the power amplifier. The regulator includes an operational amplifier comprising a loop gain control circuit and a loop gain control voltage generation circuit that supplies control voltage to the loop gain control circuit. The loop gain control voltage generation circuit minimizes a loop gain of the operational amplifier when starting up the regulator.

The present invention relates to a linear, high sensitivity, high speed trans-impedance amplifier (TIA) which allows a large dynamic range of input current up to very large values, maintains high linearity and keeps constant output voltage, maintains the same frequency response across the full gain control range, provides very high input sensitivity and large bandwidth, and allows input current monitoring without affecting input sensitivity. In other words, the novel circuit disclosed herein provides for the feedback path to maintain the same level of feedback even while the output signal is varied. This allows a wide and stable bandwidth, as well as a monitor to be placed in the TIA.