Apparatus and methods for vector modulator phase shifters are provided. In certain embodiments, a phase shifter includes a quadrature filter that filters a differential input signal to generate a differential in-phase (I) voltage and a differential quadrature-phase (Q) voltage, an in-phase variable gain amplifier (I-VGA) that amplifies the differential I voltage to generate a differential I current, a quadrature-phase variable gain amplifier (Q-VGA) that amplifies the differential Q voltage to generate a differential Q current, and a current mode combiner that combines the differential I voltage and the differential Q voltage to generate a differential output signal. A phase difference between the differential output signal and the differential input signal is controlled by gain settings of the I-VGA and the Q-VGA.

Amplifiers, amplification circuits, and phase shifters, for example, for flexibly adjusting an output phase to thereby meet a requirement of a constant phase on a link in a communications field, are provided. In one aspect, an amplifier includes first, second, and third MOS transistors. The first MOS transistor includes a gate separately coupled to a signal input end and a bias voltage input end, a source coupled to a power supply, and a drain separately coupled to sources of the second and third MOS transistors. A drain of the third MOS transistor is coupled to a ground, and a drain of the second MOS transistor is coupled to a signal output end. The bias voltage input end is configured to receive a bias voltage to adjust a phase difference between an input signal at the signal input end and an output signal at the signal output end.

Disclosed herein are methods for use in operating signal amplifiers that provide impedance adjustments for different gain modes. The impedance adjustments are configured to result in a constant real impedance for an input signal at the amplifier. Some of the disclosed methods adjust impedance using switchable inductors to compensate for changes in impedance with changing gain modes. Some of the disclosed methods adjust a device size to compensate for changes in impedance with changing gain modes. By providing impedance adjustments, the amplifiers reduce losses and improve performance by improving impedance matching over a range of gain modes.

A low noise amplifying system with adjustable gain. The low noise amplifier includes a plurality of gain stages, including a first stage and a last stage each having fixed gain, and an intermediate stage having adjustable gain. The intermediate stage is an inverting gain stage that includes a field effect transistor connected from the output to the input, to provide negative feedback, reducing the gain as a control voltage (applied to the gate of the field effect transistor) is adjusted to decrease the channel resistance of the field effect transistor. A control circuit measures the input and output signal power of the amplifying system and adjusts the gain of one or more intermediate stages to trade off linearity against noise figure.

The present invention discloses a signal output circuit having DC gain maintaining mechanism used in an image signal transmission apparatus that includes a front-stage driving circuit and a back-stage driving circuit. The front-stage driving circuit includes a continuous time linear equalizer (CTLE) having an adjusting capacitor and configured to receive a digital input signal to perform a high frequency enhancement thereon to increase a bandwidth of the digital input signal to generate a front-stage output signal. The back-stage driving circuit includes a CTLE without the adjusting capacitor and configured to increase a DC gain of the front-stage output signal to compensate a DC gain drop between the front-stage output signal and the digital input signal to generate a back-stage output signal to an image signal receiving apparatus.

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.

An amplifying device includes a radio frequency (RF) signal input terminal to which an RF signal is input, a buffer circuit, a linearizer including a transistor, a power amplifier, and a control circuit. The control circuit outputs a first gate voltage when a level of the RF signal input is a first level, the first gate voltage causing the transistor to perform a class B operation. The control circuit outputs a second gate voltage when the level of the RF signal is a second level higher than the first level, the second gate voltage causing the transistor to perform a class AB operation. Output impedance of the buffer circuit that is seen from an input side of the linearizer is set such that a reflection loss of the RF signal input from the buffer circuit to the linearizer is a predetermined level or less.

A number of biasing circuits for amplifiers including voltage controlled amplifier is presented. Also a number of field effect transistor circuits include voltage controlled attenuators or voltage controlled processing circuits. Example circuits include modulators, lower distortion variable voltage controlled resistors, sine wave to triangle wave converters, and or servo controlled biasing circuits.

Methods related to amplification of radio-frequency signals. In some embodiments, a method for amplifying a radio-frequency signal can include configuring a gain stage to be in a selected one of a plurality of gain settings, with at least some of the gain settings resulting in different phases for the radio-frequency signal. The method can further include adjusting the phase of the radio-frequency signal for the selected gain setting, such that the adjusted phase is part of desired phases adjusted from the different phases.

Described herein are variable gain amplifiers and multiplexers that embed programmable attenuators into switchable paths to provide variable gain for individual amplifier inputs. The variable gain for an individual input is provided using an amplification stage that is common for each input of the amplifier. A variable attenuation is provided for individual inputs through a combination of a band selection switch and an attenuation selection branch. Individual inputs can be configured to bypass the variable attenuation in a high gain mode.