An exemplary improved ground for a power amplifier circuit may include structural separation of the drive amplifier and the power amplifier grounds and cut-off of the power amplifier induced feedback current to ensure stability under a wide-range of operating conditions. The exemplary power amplifier may include a first ground coupled to a first amplifier circuit, a second ground coupled to a second amplifier circuit separate from the first ground, and the first amplifier circuit generates a drive current for the second amplifier circuit.

A receiver circuit comprising: an input-pin; a receiver-input-node; a ground-pin; an internal-node that is connected to the input-pin; and a MOSFET. The MOSFET has a conduction channel connected in series between the internal-node and the receiver-input-terminal; and a gate terminal, the voltage at which sets the conductivity of the conduction channel. The receiver circuit also includes an amplifier that: has an input terminal that is connected to the internal-node; and provides a voltage control signal to the gate terminal of the MOSFET such that the voltage at the internal-node with respect to the ground-pin is constant.

A power-on reset (POR) circuit includes: a signal generator circuit for generating a first and a second signal according to an input voltage, and a comparator circuit. The comparator circuit, having a non-zero input offset, includes a first MOS transistor with a first conductive type and having a first conductive type gate and a first threshold voltage, and a second MOS transistor with a first conductive type and having a second conductive type gate and a second threshold voltage. The input offset relates to a difference between the first and the second threshold voltage. The first and the second signal control the first and the second MOS transistors respectively to generate a POR signal. When the input voltage exceeds a POR threshold which relates to a predetermined multiple or ratio of the input offset, the POR signal transits its state.

Techniques are described for ground-intermediating buffering that can effectively use the reference grounds of the circuit domains on either side of a buffer stage to generate one or more intermediated grounds for one or more signal buffers. For example, one of the reference grounds has a first amount of ground noise, the other of the reference grounds has a second amount of ground noise that is greater than or less than the first amount, and the intermediated grounds are generated to have respective amounts of ground noise that are between the first and second amounts. The ground intermediating buffer can perform signal buffering with respect to the intermediated ground(s), thereby reducing ground noise coupling across the circuit domains through both the signal and ground paths of the buffer stage.

Apparatus and methods for power amplifiers isolated by differential ground are provided. In certain implementations, a mobile device includes a transceiver that generates a plurality of radio frequency input signals including a first radio frequency input signal and a second radio frequency input signal, and a plurality of differential power amplifiers including a first differential power amplifier that provides amplification to the first radio frequency input signal and a second differential power amplifier that provides amplification to the second radio frequency input signal. The first differential power amplifier and the second differential power amplifier each operate with differential ground so as to provide isolation between the first differential power amplifier and the second differential power amplifier.

A power-on reset (POR) circuit includes: a signal generator circuit for generating a first and a second signal according to an input voltage, and a comparator circuit. The comparator circuit, having a non-zero input offset, includes a first MOS transistor with a first conductive type and having a first conductive type gate and a first threshold voltage, and a second MOS transistor with a first conductive type and having a second conductive type gate and a second threshold voltage. The input offset relates to a difference between the first and the second threshold voltage. The first and the second signal control the first and the second MOS transistors respectively to generate a POR signal. When the input voltage exceeds a POR threshold which relates to a predetermined multiple or ratio of the input offset, the POR signal transits its state.

Apparatus and methods for power amplifier systems with differential ground are provided. In certain implementations, a semiconductor die for a radio frequency communication system includes a differential ground network configured to distribute a ground voltage. The differential ground network is substantially symmetric with respect to a line of symmetry. The semiconductor die further includes a first differential power amplifier including a first half circuit and a second half circuit that operate differentially to provide amplification. The first half circuit and the second half circuit are symmetrically connected to the differential ground network. The semiconductor die can further include a second differential power amplifier, and the differential ground network serves to provide isolation between the first differential power amplifier and the second differential power amplifier.

An exemplary improved ground for a power amplifier circuit may include structural separation of the drive amplifier and the power amplifier grounds and cut-off of the power amplifier induced feedback current to ensure stability under a wide-range of operating conditions. The exemplary power amplifier may include a first ground coupled to a first amplifier circuit, a second ground coupled to a second amplifier circuit separate from the first ground, and the first amplifier circuit generates a drive current for the second amplifier circuit.

The invention provides a grounding structure and a grounding method for a vacuum tube audio amplifier, the grounding structure and the grounding method including: with respect to a power source, utilizing a power circuit without a choke, an anti-coupling circuit, and a filament voltage regulator circuit; and with respect to the grounding method, utilizing an negative output terminal of an audio output transforming circuit or a negative terminal of a filter capacitor in the power circuit as a single ground terminal of the vacuum tube audio amplifier, and not arranging a grounding metal bottom plate therein, in order to achieve a compact, lightweight desktop model of a vacuum tube audio amplifier.

Apparatus and methods for power amplifier systems with differential ground are provided. In certain implementations, a semiconductor die for a radio frequency communication system includes a differential ground network configured to distribute a ground voltage. The differential ground network is substantially symmetric with respect to a line of symmetry. The semiconductor die further includes a first differential power amplifier including a first half circuit and a second half circuit that operate differentially to provide amplification. The first half circuit and the second half circuit are symmetrically connected to the differential ground network. The semiconductor die can further include a second differential power amplifier, and the differential ground network serves to provide isolation between the first differential power amplifier and the second differential power amplifier.