To provide a variable gain amplifier capable of correcting a DC offset voltage through simpler control even when a gain thereof is changed. A differential output type variable gain amplifier is equipped with a first voltage correction unit coupled to a preceding stage of a variable gain amplifier circuit and for outputting a first correction voltage to correct a potential difference generated between a first conductor provided with a first input resistor and a second conductor provided with a second input resistor, and a second voltage correction unit coupled to a subsequent stage of the variable gain amplifier circuit and for correcting a differential output. A control unit is configured to control the first correction voltage and a correction amount of a potential difference by the second voltage correction unit and thereby attenuate a DC offset voltage included in the differential output.

An automatic gain control (AGC) attenuator for an amplifier. In one example, the AGC attenuator includes a first transistor stack including a plurality of first banks of current steering differential transistor pairs and configured to receive a radio frequency (RF) input signal and output a first attenuated RF signal. Each first bank of the plurality of first banks is configured to attenuate the RF input signal by a predetermined value. The AGC attenuator also includes a second transistor stack that includes a plurality of second banks of current steering differential transistor pairs. The second transistor stack is cascoded to the first transistor stack, and is configured to receive the first attenuated RF signal and output a second attenuated RF signal. Each second bank of the plurality of second banks is configured to attenuate the first attenuated RF signal by a predetermined value.

An RF transceiver front-end circuit includes an antenna, a first transceiving switch, a reception processing unit, a transmission processing unit and a transmission unit. The reception processing unit includes a low-noise amplifier, a first variable gain amplifier at a back-end circuit of the low-noise amplifier, and a first phase shifter at a back-end circuit of the first variable gain amplifier, wherein a phase of the first variable gain amplifier is constant. The transmission processing unit includes a power amplifier, a second phase shifter at a front-end circuit of the power amplifier, and a second variable gain amplifier at a front-end circuit of the second phase shifter, wherein a phase of the second variable gain amplifier is constant. The transmission unit includes a transmission line and a plurality of passive phase adjustors controlled to change a phase shifting angle of a signal on the transmission line.

Disclosed herein are signal amplifiers that have an input impedance that varies over different bias currents. The signal amplifier includes a gain stage with a plurality of switchable amplification branches that are each capable of being activated such that one or more of the activated amplification branches provides a targeted adjustment to the input impedance. In addition, disclosed herein are signal amplifiers that have a variable-gain stage configured to provide a plurality of gain levels that result in different input impedance values presented to a respective signal by the variable-gain stage. The variable-gain stage can include a plurality of switchable amplification branches that provide a targeted adjustment to the respective input impedance values. The variable-gain stage can include a plurality of switchable inductive elements that are configured to be activated to provide a targeted adjustment to the respective input impedance values.

A signal input from a microphone is A-D converted by an A-D converter, is frequency differentiated by a pre-emphasis circuit, and is input to a shift control circuit. The shift control circuit includes a limiter circuit, a phase shifter, and a harmonic suppressor. The limiter circuit performs amplitude limitation so as to limit the amplitude of the input control target signal to be equal to or less than a first threshold. The phase shifter shifts, for the control target signal having the amplitude limited, a phase of a frequency component within the predetermined frequency range. The harmonic suppressor suppresses, for the control target signal phase-shifted by the phase shifter, a frequency component equal to or greater than a second threshold, and outputs an information signal that is the control target signal having the frequency component of equal to or greater than the second threshold suppressed. The modulator performs frequency modulation on a carrier wave in accordance with the information signal. The transmitter produces a transmission signal from the frequency-modulated carrier wave, and transmits the transmission signal via an antenna.

An apparatus includes an amplifier and a gain control circuit. The amplifier may be configured to provide multiple gain steps. The gain control circuit may be configured to provide fast and precise changes between the multiple gain steps of the amplifier. The gain control circuit may be further configured to change an impedance of the amplifier to switch between the gain steps. The gain control circuit may be further configured to compensate for changes in frequency response related to changing the impedance. The gain control circuit may be further configured to inject a complementary charge to an input of the amplifier to correct a bias voltage deviation and a transient caused by the gain control circuit.

A shift control circuit includes a first limiter circuit, a phase shifter, a first suppressor, and a reducer. The first limiter circuit limits the amplitude of a control target signal input from a microphone, having undergone A-D conversion by an A-D convener, and frequency differentiation by a pre-emphasis circuit, and having the relative intensity of harmonic components increased. The phase shifter performs, for the control target signal having undergone the amplitude limitation, phase shift on the frequency component within a first frequency range. The first suppressor suppresses, for the control target signal having undergone the phase shift, the frequency component equal to or greater than a second threshold. The reducer suppresses, for the control target signal having the suppressed frequency component, the frequency component within a second frequency range, and outputs as an information signal. A modulator performs frequency modulation on a carrier wave in accordance with the information signal, and a transmitter produces a transmission signal from the carrier wave having undergone the frequency modulation, and transmits the transmission signal via an antenna.

Embodiments of the disclosure relate to a frequency selective low noise amplifier (LNA) circuit, which includes a transconductive LNA(s). In one aspect, filter circuitry is provided in a degeneration path of a transconductive LNA(s) to pass in-band frequencies and reject out-of-band frequencies by generating low impedance and high impedance at the in-band frequencies and the out-of-band frequencies, respectively. However, having the filter circuitry in the degeneration path may cause instability in the transconductive LNA. As such, a feedback path is coupled between an input node of the transconductive LNA(s) and the degeneration path to provide a feedback to improve stability of the transconductive LNA(s). In addition, the feedback can help improve impedance match in the frequency selective LNA circuit. As a result, the transconductive LNA(s) is able to achieve improved noise figure (NF) (e.g., below 1.5 dB), return loss, linearity, and stability, without compromising LNA gain.

Disclosed is a broadcast receiver that includes an antenna connector configured to connect with an antenna for receiving a broadcast signal including broadcast content. The broadcast receiver also includes a signal processor configured to generate a reference signal having a strength corresponding to a signal input through the antenna connector and to process the generated reference signal to output an image signal for displaying the broadcast content, and a controller configured to determine whether the antenna is connected to the antenna connector based on an output value of the reference signal and to perform subsequent operations related to whether the antenna is connected based on the determination.

A shift control circuit includes a first limiter circuit, a phase shifter, a first suppressor, and a reducer. The first limiter circuit limits the amplitude of a control target signal input from a microphone, having undergone A-D conversion by an A-D convener, and frequency differentiation by a pre-emphasis circuit, and having the relative intensity of harmonic components increased. The phase shifter performs, for the control target signal having undergone the amplitude limitation, phase shift on the frequency component within a first frequency range. The first suppressor suppresses, for the control target signal having undergone the phase shift, the frequency component equal to or greater than a second threshold. The reducer suppresses, for the control target signal having the suppressed frequency component, the frequency component within a second frequency range, and outputs as an information signal. A modulator performs frequency modulation on a carrier wave in accordance with the information signal, and a transmitter produces a transmission signal from the carrier wave haying undergone the frequency modulation, and transmits the transmission signal via an antenna.