Techniques are described for crest factor reduction in power amplifier circuits. For example, crest factor reduction can keep the peak signal level of a signal for transmission to below a peak threshold level associated with a power amplifier in the transmission path. The signal is received by the crest factor reduction system and clipped in accordance with the peak threshold level. Edge smoothing is then applied to the clipped signal to reduce out-of-band emissions. The edge smoothing is implemented by a moving average filter, such as a time-domain box filter. In some embodiments, a maximum operation or minimum operation is used to prevent signal peak regrowth after the filtering. Some embodiments also include various iteration loops to further improve crest factor reduction.

A voltage controlled amplifier with an amplitude limiting circuit, such as a clip limiter, that is separate from the signal path on which the input signal is received by a power amplifier can reduce both noise and power expenditure of the voltage controlled amplifier. The amplitude limiting circuit can include a transistor network that is controlled by a pair of utility operational amplifiers. These utility amplifiers may use less current than the audio amplifier of the voltage controlled amplifier. Further, the transistor network can be deactivated when a signal supplied to the voltage controlled amplifier is below a clipping or other voltage limiting threshold.

A circuit comprising: an input terminal configured to receive an input-signal; an output terminal configured to provide an output-signal; a reference circuit comprising: a first output terminal configured to provide a first-reference-signal; a second output terminal configured to provide a second-reference-signal; and a third output terminal configured to provide a third-reference-signal. A comparator-block configured to compare a comparator-input-voltage-signal representative of signalling received at the input terminal with: (i) the first-reference-signal, (ii) the second-reference-signal and (iii) the third-reference-signal in order to generate a comparison-signal. A control-block configured to set the output-signal as one of at least two voltage levels based on the comparison-signal; and an input-control-circuit configured to apply a feedback-control-signal to the input-terminal based on the comparison-signal.

Techniques are described for crest factor reduction in power amplifier circuits. For example, crest factor reduction can keep the peak signal level of a signal for transmission to below a peak threshold level associated with a power amplifier in the transmission path. The signal is received by the crest factor reduction system and clipped in accordance with the peak threshold level. Edge smoothing is then applied to the clipped signal to reduce out-of-band emissions. The edge smoothing is implemented by a moving average filter, such as a time-domain box filter. In some embodiments, a maximum operation or minimum operation is used to prevent signal peak regrowth after the filtering. Some embodiments also include various iteration loops to further improve crest factor reduction.

A source follower with an input node and an output node includes a first transistor, a second transistor, and a DC (Direct Current) tracking circuit. The first transistor has a control terminal, a first terminal coupled to a first node, and a second terminal coupled to a second node. The second transistor has a control terminal, a first terminal coupled to a ground voltage, and a second terminal coupled to the first node. The DC tracking circuit sets the second DC voltage at the second node to a specific level. The specific level is determined according to the first DC voltage at the first node. The output node of the source follower is coupled to the first node.

A new method for amplifying signals having higher bandwidth, lower T.H.D., higher efficiency, smaller circuit size and lower costs in design, has been developed. A clipped signal is amplified to smaller pieces and each smaller part is amplified. Adding clipped amplified signals to each other, the main amplified signal is generated.

Mechanisms for evaluating amplitude for current pulses provided to a transimpedance amplifier (TIA) for current levels beyond the linear range of the TIA where clipping circuit(s) may limit the input voltage of the TIA are disclosed. In one aspect, an example TIA arrangement includes a clipping arrangement that includes multiple clipping circuits. Each clipping circuit can be biased by different bias voltages such that the different clipping circuits are activated at different input current amplitudes. Different clipping circuits can have different impedances, which can result in different recovery time characteristics. With the multiple clipping circuits in clipping arrangements discussed herein, a saturated dynamic range of a TIA can be divided into sub-regions and different pulse widening characteristics for each region may be defined, which may enable determination of amplitude for current pulses provided to the TIA even for current levels beyond the linear range of the TIA.

The disclosed embodiments include an audio amplifier system configured to provide a total harmonic distortion (THD) controlled clip detector and an automatic gain limiter (AGL) solution for a closed-loop amplifier. The audio amplifier system is capable of maintaining high power output without hard distortion (i.e., hard clipping) for providing better acoustics, while preventing damage to the system.

A source follower with an input node and an output node includes a first transistor, a second transistor, and a DC (Direct Current) tracking circuit. The first transistor has a control terminal, a first terminal coupled to a first node, and a second terminal coupled to a second node. The second transistor has a control terminal, a first terminal coupled to a ground voltage, and a second terminal coupled to the first node. The DC tracking circuit sets the second DC voltage at the second node to a specific level. The specific level is determined according to the first DC voltage at the first node. The output node of the source follower is coupled to the first node.

A control device includes: a differential amplification circuit that amplifies a difference with respect to an input signal; and a clipping circuit that is connected to an output side of the differential amplification circuit and clips an input voltage. The differential amplification circuit includes a plurality of switching elements formed of a GaN semiconductor, and the clipping circuit includes a switching element formed of the GaN semiconductor.