A computer sound card includes a power supply noise isolation circuit for reducing ground plane noise generated during application of heavy electrical loads to the power supply, such as loads presented by computer GPUs. The power supply isolation circuit isolates the output ground from the ground presented from the power supply to the isolation circuit input. The isolation circuit in one embodiment includes switching circuitry and a transformer to reduce the power supply ripple noise that might otherwise be introduced by the power supply into an amplifier such as a microphone preamp. In some embodiments a differential amplifier stage is added to the output of the microphone preamp stage to further reduce noise, such as common mode noise.

A differential feedback circuit with an active noise cancelation technique using a dual input differential pair. In the differential feedback circuit, a feedback voltage and a reference voltage connect to a primary input pair. Sensed noise at the inputs is put to a secondary input pair of the differential amplifier, which is inverted with respect to the primary input pair. In other words, the reference voltage, which may be subject to noise, connects directly to one terminal of the secondary input pair and through a low-pass filter to another terminal of the secondary input pair so that the noise, which may be coupled to the differential feedback circuit, cancels at the output of the differential feedback circuit.

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 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.

An amplifying device includes first and second substrates. The first substrate has a first mounting surface, and the second substrate has a second mounting surface. The first mounting surface of the first substrate that is opposite the second substrate is provided with: a first ground line; a first signal line configured to transfer an audio signal; and a first amplifier configured to amplify the audio signal. The second mounting surface of the second substrate that is opposite the first substrate is provided with: a second grounded line; a second signal line configured to transfer an audio signal; and a second amplifier configured to amplify the audio signal. The first and second grounded lines correspond to each other in position and shape, and overlap in planar view. The first and second signal lines correspond to each other in position and shape, and overlap in planar view.

An amplifying device includes first and second substrates. The first substrate has a first mounting surface, and the second substrate has a second mounting surface. The first mounting surface of the first substrate that is opposite the second substrate is provided with: a first ground line; a first signal line configured to transfer an audio signal; and a first amplifier configured to amplify the audio signal. The second mounting surface of the second substrate that is opposite the first substrate is provided with: a second grounded line; a second signal line configured to transfer an audio signal; and a second amplifier configured to amplify the audio signal. The first and second grounded lines correspond to each other in position and shape, and overlap in planar view. The first and second signal lines correspond to each other in position and shape, and overlap in planar view.

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 multiple-stage amplifier includes a driver stage die and a final stage die. The final stage die includes a III-V semiconductor substrate (e.g., a GaN substrate) and a first transistor. The driver stage die includes another type of semiconductor substrate (e.g., a silicon substrate), a second transistor, and one or more secondary circuits that are electrically coupled to a control terminal of the first transistor. A connection (e.g., a wirebond array or other DC-coupled connection) is electrically coupled between an RF signal output terminal of the driver stage die and an RF signal input terminal of the final stage die. The secondary circuit(s) of the driver stage die include a final stage bias circuit and/or a final stage harmonic control circuit, which are electrically connected to the final stage die through various connections.

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.

Embodiments herein include a replica communication path and monitor circuit to provide increased common mode transient immunity. As its name suggests, the monitor circuit monitors the replica communication path and produces an adjustment signal (common mode transient adjustment signal) to cancel presence of a common mode transient signal in one or more other communication paths conveying data signals.