Abstract: A radio frequency device comprises a radio frequency (RF) power amplifier (PA) operably coupled to a protection circuit for minimising voltage standing wave ratio effects, wherein the protection circuit comprises a current limiter indexed to a power supplied to the RF PA. In this manner, the protection circuit combines detection of both current and voltage increase in order to provide a direct feedback on the final RF PA stage via a bias control.

Abstract: In one embodiment, the present invention includes an amplifier having an input to receive a radio frequency (RF) signal from an output node of a source. An input stage coupled to the amplifier input may include one or more components to aid in processing of incoming signals. One such component coupled between the source and the input of the amplifier is a coupling capacitor used to maintain a bias voltage of the amplifier at a different potential than a DC voltage of the output node. In certain applications, the amplifier and the coupling capacitor may be integrated on a single substrate.

Abstract: An amplifier system includes an instrumentation amplifier arrangement being designed to amplify the difference between two voltage inputs with a defined gain, and to produce a single-ended output referenced to a known reference point. A front end circuit is coupled to the instrumentation amplifier. The front end circuit is configured to include a current clamp to actively limit the current in a gain resistor of the instrumentation amplifier to prevent input currents flowing when the instrumentation amplifier is over-driven.

Abstract: Methods and apparatus to detect impedance at an amplifier output are described. In one example, a method of determining a relative value of an amplifier output load may include determining a current provided to the amplifier output load in response to an input signal; determining a current provided to a reference load in response to a signal based on the input signal; comparing the current provided to the amplifier output load to the current provided to the reference load; and indicating a relationship between the amplifier output load and the reference load based on the current provided to the amplifier output load and the current provided to the reference load.

Abstract: A patterning area of an output circuit is reduced while securing strong enough ESD tolerance. In the output circuit of this invention, an output of a first amplifier and an output of a second amplifier are connected to a common output pad. Each of the amplifiers is driven by each of signals ?1 and ?2 from an internal circuit, respectively. The first amplifier has larger driving capacity than the second amplifier. A high voltage side power supply terminal of the second amplifier is provided with a power supply voltage VDD from a power supply pad through a first protection resistor, while a low voltage side power supply terminal of the second amplifier is provided with a ground voltage VSS from a ground pad through a second protection resistor. And a third protection resistor is connected between an output of the second amplifier and an output terminal. The first, second and third protection resistors are made of metal wirings, and their resistance is preferably about 10?.

Abstract: The present invention provides a power amplifier system that includes a power terminal, a ground terminal, an output terminal, a ripple terminal, a control terminal, a power amplifier circuit connected between the power terminal and the ground terminal, a negative potential detection circuit connected to the output terminal, a bias start-up circuit that is controlled by an input of the control terminal, an output of the negative potential detection circuit, and the potential of the ripple terminal, and controls a bias start-up signal, a power amplifier IC that has a bias circuit which is controlled to be started up by the bias start-up signal, and has its output node for outputting a power amplifier bias voltage connected to the ripple terminal, and a ripple filter capacitor externally connected to the ripple terminal of the power amplifier IC.

Abstract: A procedure for operation of a high frequency amplifier having a power transistor—amplifier stage designed as a source or emitter circuit for amplifying a gate or base side high frequency signal supplied over an input interface network E which signal is amplified at the drain or collector side and output via an output interface network. A device for the measurement of the drain or collector current I_D is connected at the amplifier stage on the drain or collector side and a final control element is connected on the gate or base side. A pre-adjustable desired value W_SOLL and an actual value W_IST corresponding to the drain or collector current are input to the final control element, which adjusts the gate voltage or the base current so that the drain or collector current I_D is brought to the desired value W_SOLL. At a constant input power P_IN of the high frequency amplifier, the envelope curve of the output signal RF_OUT is modulated by the desired value W_SOLL.

Abstract: In the present invention, in parallel with a resistor which determines an amplification rate being fed back from an output to an input of an output stage OP amp in an audio amplifier circuit, providing a first diodes connected bi-directionally together with a first switch circuit, the output voltage of the output stage OP amp is limited to a voltage, when the first diodes are turned ON. The limit voltage of the first diodes corresponds to a speaker having a low withstand voltage. Accordingly, through ON/OFF of the first switch circuit, a power output from the output stage OP amp can be selected depending on the withstand voltage of a speaker to be connected.

Abstract: A protection circuit of a digital amplifier includes a DC voltage detection circuit for detecting a DC voltage occurring in a loudspeaker output terminal; a control circuit for performing protection operation when the DC voltage detection circuit outputs a detection signal; and a midpoint potential detection circuit for detecting midpoint potential shift between a positive power supply voltage and a negative power supply voltage. Output of the midpoint potential detection circuit is connected to input of the DC voltage detection circuit and when the midpoint potential shift is detected, the DC voltage detection circuit outputs a detection signal.

Abstract: In one embodiment, the present invention includes an amplifier having an input to receive a radio frequency (RF) signal from an output node of a source. An input stage coupled to the amplifier input may include one or more components to aid in processing of incoming signals. One such component coupled between the source and the input of the amplifier is a coupling capacitor used to maintain a bias voltage of the amplifier at a different potential than a DC voltage of the output node. In certain applications, the amplifier and the coupling capacitor may be integrated on a single substrate.

Abstract: A method and apparatus are provided for use with a power amplifier for protecting active devices on the power amplifier. A peak detector is used by control circuitry to detect the presence of a peak voltage that exceeds a threshold voltage. In response to the detection of a peak voltage, the gain of the power amplifier is reduced.

Abstract: A transistor biasing circuit is shown that utilizes a negative feedback loop control circuit to set the gate bias voltage in the output transistors of a power amplifier. This control circuit has a current sensor in series with the drain of the transistor, the current sensor output in turn feeding a dc signal into a dc amplifier, and the output of the dc amplifier driving a gate bias integrator which forms a dc control loop for maintaining the bias point. The output transistor is protected from excessive temperature and/or excessive power dissipation.

Abstract: An amplifier for improving an electrostatic discharge (ESD) characteristic includes an operational amplifier, a first resistor circuit, a first fuse box, a second resistor circuit, and a second fuse box. The operational amplifier includes a first input terminal receiving a first input signal, a second input terminal receiving a second input signal, and an output terminal outputting an output signal. The first resistor circuit is connected between the second input terminal and a first node to prevent ESD from being input to the second input terminal. The first fuse box is connected between the first node and the output terminal of the operational amplifier. The second resistor circuit is connected between the second input terminal and a second node to prevent ESD from being input to the second input terminal. The second fuse box is connected between the second node and a terminal for receiving a ground voltage.

Abstract: In an embodiment of this invention, if a state, in which duty ratio of a PWM signal is kept equal to or greater than a predetermined value, has been maintained for a first time period, the duty ratio of the PWM signal of a digital power amplifier is adjusted downward. Furthermore, the duty ratio of the PWM signal is maintained without change when the duty ratio of the PWM signal is adjusted downward for a second time period, and the duty ratio of the PWM signal is adjusted downward only when volume is set to a maximum value allowable in the power amplifier. Accordingly, the temperature of the power amplifier can be prevented from rapidly increasing, the internal temperature of an electronic apparatus can be efficiently prevented from increasing, and damage to the power amplifier resulting from increased temperature can be prevented.

Abstract: An apparatus and method is disclosed for providing control of current consumption of a power amplifier. The power amplifier comprises an output stage for amplifying a RF signal, and the output stage is operably coupled to an output load. The power amplifier further comprises a bias circuit operably coupled to the output stage, wherein the bias circuit is capable of applying a bias voltage to the output stage. The power amplifier still further comprises a limit circuit operably coupled to the bias circuit for detecting an increase in the current of the output stage under an output load mismatch and in response, decreasing the bias voltage applied to the output stage.

Abstract: A output offset protection circuit provides protection of the load and the power amplifier through monitoring the temperature of the power transistor in the operational amplifier to detect fault conditions of an output block. In the output offset protection circuit, a sensor block monitors the temperature differences between the power transistors, while the output block is driving the load. Upon detection of the temperature differences reaching a 1st threshold level, the cutoff block sends a cutoff signal to a protection switch block, and the hysteresis block is activated. The hysteresis block shifts the threshold level lower to the 2nd threshold level. The sensor block continues to monitor the temperature differences until the 2nd threshold level is reached. Then the cutoff block is deactivated.

Abstract: In a method of detecting a fault in a class D amplifier, an amplifier output signal is generated based on inverting a pulse width modulation signal corresponding to received audio data. The amplifier output signal is low pass filtered and hysteretically filtered (Schmitt Triggered). The filtered amplifier output signal is sampled (latched) using the pulse width modulation signal as a sampling (latch) clock signal, to generate a first comparison signal. The pulse width modulation signal is sampled (latched) using the filtered amplifier output signal as a sampling (latch) clock signal, to generate a second comparison signal. A fault detection signal for detecting the fault is generated by comparing the first and second comparison signals. Since the first pulse width modulation signal and the filtered amplifier output signal are robustly compared, a fault occurrence may be directly and reliably detected.

Abstract: An adjustable power amplifier includes an input capacitor, an input transistor, an inductor, an output capacitor, and a gain module. The input capacitor includes a first plate and a second plate, wherein the first plate of the input capacitor is operably coupled to receive an input radio frequency (RF) signal. The input transistor includes a gate, a drain, and a source, wherein the gate of the input transistor is operably coupled to the second plate of the input capacitor and the source of the input transistor is operably coupled to a circuit ground. The inductor includes a first node and a second node, wherein the first node of the inductor is operably coupled to a power supply and the second node of the inductor is operably coupled to the drain of the input transistor.

Abstract: A soft saturation detection circuit for a radio frequency (“RF”) power amplifier is configured to detect the onset of soft saturation in an unambiguous and accurate manner. The circuit compares the time derivative of a voltage signal indicative of the RF output power to the time derivative of a control voltage signal for the RF power amplifier. The circuit also employs a gating mechanism that ensures that a soft saturation indication signal is generated under appropriate operating conditions.

Abstract: Systems and methods for over-current protection in all-digital amplifiers using low-cost current sensing mechanisms. An over-current hard clipping unit receives a digital audio signal, clips the signal according to a clip level, and provides the signal to a modulator. The modulator modulates the signal to produce, e.g., a PWM signal and provides the modulated signal to an output stage which generates an output current to drive a speaker. An over-current sensing unit is compares the output current to a threshold value and generates a binary signal indicating whether the output current exceeds the threshold value. The hard clipping unit receives the binary signal and ramps down the clip level during time periods in which the binary signal indicates that the output current exceeds the threshold. When the binary signal indicates that the output current does not exceed the threshold value, the hard clipping unit ramps up the clip level.

Abstract: Method and apparatus are provided for protecting radio frequency (RF) power amplifiers. A circuit (10) is provided for limiting a supply current to a first stage (Q3) of the RF power amplifier having a second stage (Q2) coupled to the first stage. The circuit comprises a comparator (14) having first and second inputs and an output, and a switching circuit (12, 20, 22, 24) having an input coupled to the output of the comparator (14) and having an output configured to couple to the first stage (Q3). The first input of the comparator (14) is configured to receive the supply current, and the second input is configured to receive a current supplied to the second stage (Q2). The comparator (14) is configured to compare a ratio of the supply current to the first stage to the current supplied to the second stage (Q2) with a predetermined value. The switching circuit (12, 20, 22, 24) is configured to limit the supply current to the first stage (Q3) when the ratio exceeds the predetermined value.

Abstract: A drive signal that matches the bias of a transistor is generated. A differential amplifier calculates the difference between a specified voltage of negative power supply and another input signal. Then, a resistor that realizes a pull-down function level-shifts it towards a negative power supply voltage having a higher absolute voltage value to generate another differential signal, which is in turn amplified in another amplifier, to generate another drive signal that matches the bias of another transistor. Respective current mirror circuits detect a falling voltage occurring at both ends of a resistor connected between the transistor and the higher positive power supply voltage and a falling voltage occurring at both ends of a resistor connected between the other transistor and the higher negative power supply voltage, respectively. Then, the presence of an excessive electric current is detected by generating electric currents in accordance with to the falling voltages.

Abstract: A power amplifier protection circuit that includes protection circuitry to variably shunt an input radio frequency (RF) signal to AC ground, turn off bias to an output transistor of a power amplifier, and turn off the output transistor. The power amplifier protection circuit features an asymmetrical control that can quickly shut off a power amplifier, and turn on the power amplifier at a steady, controlled rate when an output transistor exceeds a predetermined threshold voltage.

Abstract: A radio frequency (RF) power amplification circuit including a power amplifier is provided for preventing breakdown of the power amplifier. The power amplifier includes an input for receiving RF signals and an output for providing amplified RF signals. The RF power amplification circuit also includes a bias circuit coupled to the input of the power amplifier to permit normal operation of the power amplifier when the base current is below a predetermined current threshold and to prevent normal operation of the power amplifier when the base current is above the predetermined current threshold.

Abstract: A differential receiver circuit. In one embodiment, the circuit includes first and second input transistors, each having a first terminal coupled to a bias node (a first and second bias node, respectively), as well as first and second bias transistors, each having a first terminal coupled to the first and second bias nodes, respectively. The circuit further includes a first current source coupled to provide current to the first bias node and a second current source coupled to the second bias node. The differential receiver circuit is coupled to first and second, which receive first and second voltages, respectively. The first and second current sources provide current to the first and second bias nodes, respectively, such that the voltage present on the first and second bias nodes remains with approximately a threshold voltage of a midpoint between the voltages present on the first and second voltage nodes.

Abstract: A differential input operational amplifier has a voltage clamp differential transistor pair coupled to an input differential transistor pair of the operational amplifier. The voltage clamp differential transistor pair limits the output voltage of the operational amplifier by taking over control of the operational amplifier circuits from the input differential transistor pair as the output voltage approaches a clamp voltage value. A reference voltage may be used to set the output voltage at which the input differential transistor pair will be clamped by the voltage clamp differential transistor pair. Below the clamp voltage, operation of the input differential transistor pair will not be affected. At the clamp voltage the input differential transistor pair will no longer control the output of the differential amplifier, rather the voltage clamp differential transistor pair will control the maximum voltage output of the differential amplifier.

Abstract: In one embodiment, a method is provided for reducing output current oscillations of a driver provided with i) a current sensing circuit that senses excessive current draws of an output stage of the driver, and ii) a feedback control circuit that reduces the excessive current draws. In accordance with the method, an output of the current sensing circuit is coupled to an input of a common source amplifier with source degeneration. The output of the common source amplifier is coupled to a node between an input stage and an amplification stage of the driver. The common source amplifier is configured to be activated when the current sensing circuit senses an excessive current draw of the output stage, at which time the feedback control circuit is also activated. Related apparatus is also disclosed.

Abstract: In a power amplifier driven by a pulse width modulation (PWM) signal, a first pair of drive pulses opposite in level to each other is formed from a first pulse width modulation signal whose quantization level corresponds to its pulse width and supplied to a first push-pull circuit (15). A second pair of drive pulses opposite in level to each other is formed from a second pulse width modulation signal whose two's complement of quantization level corresponds to its pulse width, and supplied to a second push-pull circuit (16). A speaker (19) is connected between the first and second push-pull circuits (15 and 16). A deviation between potentials at the output terminals of the first and second push-pull circuits (15 and 16), respectively, is detected. When a deviation is detected, the push-pull circuits are substantially stopped from operating.

Abstract: A CMOS gain stage includes biasing circuitry configured to insure saturation of a subsequent stage without a source follower circuit. The CMOS gain stage is optionally powered by a supply voltage that is greater than a permitted supply voltage for a processes technology that is used to fabricate the CMOS gain stage. In order to protect CMOS devices within the CMOS gain stage, optional drain-to-bulk junction punch-through protection circuitry is disclosed. A variety of optional features can be implemented alone and/or in various combinations of one another. Optional features include process-voltage-temperature (“PVT”) variation protection circuitry, which renders a gain relatively independent of process, voltage, and/or temperature variations. Optional features further include bandwidth enhancement circuitry.

Abstract: A directional coupler is provided on the output side of a power amplifier. An increase in reflected wave power from a load is detected through the directional coupler by an electric power detector (wave detector). Then, a detection signal of an electric power detector is provided to a power amplifier supply voltage control circuit. As a result, the supply voltage supplied to the power amplifier is reduced gradually. By virtue of this, the supply voltage provided to the power amplifier is gradually reduced when the power amplifier approaches a breakdown condition. This protects the power amplifier.

Abstract: A low noise amplifier (LNA), which utilizes an AC coupling technique that can internally bias diodes in such a way as to provide effective low noise amplification, is provided. The low noise amplifier includes an input to an amplifier circuit, and an AC coupling capacitor disposed externally to a chip boundary of the amplifier circuit.

Abstract: An amplifier (10?) has a first amplifier stage (14) for producing a control current (IX) in response to an input voltage. A second amplifier stage (16) has first (46) and second (38) transistors. The first transistor (46) is coupled to receive the control current (IX) and is operable to produce a control voltage. The second transistor (38) is coupled to receive the control voltage and operable to produce an output current. A nonlinear resistive element (50) is coupled to the first transistor (46) to add a nonlinear function of the control current (IX) to the control voltage. The nonlinear resistive element (50) may include a third transistor connected between the first transistor (46) and a reference potential, operable to receive the control current (IX) and to generate the nonlinear function thereof.

Abstract: An amplifier circuit operable to provide symmetric current limiting. The amplifier circuit includes a common source amplifier for sourcing a current and receiving an voltage input, a current source, and a current limiting device coupled between the common source amplifier and the current source. The current limiting device is operable to limit the current sourced by the common source amplifier. A bias network coupled to the current limiting device biases the current limiting device. An output is coupled to the current limiting device. The amount of current that is sourced to the output of the amplifier circuit may be limited, such that current limiting is symmetrical.

Abstract: According to one embodiment of the invention, a circuit arrangement includes a regulator circuit. The circuit arrangement further includes a current limit circuit coupled to the regulator circuit. The circuit arrangement further includes a power amplifier coupled to the regulator circuit, where the power amplifier is configured to draw a first current from the regular circuit. The current limit circuit is configured to decrease the first current when the first current causes a second current in the current limit circuit to be greater than a reference current. According to this embodiment, the second current is a mirror current of the first current. The current limit circuit includes a current sink, where the current sink is configured to sink the reference current to ground. The current limit circuit further includes a feedback loop, where the feedback loop causes the second current to be substantially equal to the reference current.

Abstract: An amplifier 3 amplifies a transmission signal, and outputs the amplified signal to an antenna. A directional coupler 6 causes a portion of power passing through a first path connecting the amplifier 3 and the antenna to branch to a second path. A detection section 7 detects an electrical parameter changing with a change in the intensity of power reflected from the antenna to the amplifier 3, thereby detecting the intensity of the reflected power. A control circuit 8 changes a proportion of power caused to branch to the second path by the directional coupler 6, based on the electrical parameter detected by the detection circuit 7. Thus, it is possible to provide a reflected power suppression circuit capable of facilitating size reduction and preventing a power amplifier from being damaged due to breakage of an antenna, while minimizing a power loss at the time of signal transmission.

Abstract: A voltage level detector (8) which activates itself by monitoring the voltage level (VSTB) at a standby pin (5) during power-up of an audio power amplifier (10), and can detect fault conditions of an output block (2), such as a short to ground at an output terminal (3), in contrast to conventional protection circuits that can operate only after power-up.

Abstract: A current threshold circuit includes a series impedance, a reference voltage source, and a comparison module. The series impedance couples an output of a current source to a load, wherein impedance of the series impedance is substantially less than impedance of the load. The reference voltage source is operably coupled to produce a reference voltage differential. The comparison module is operably coupled to compare the reference voltage differential with a differential voltage of the series impedance, wherein the comparison module generates an excessive current indication when the differential voltage of the series impedance compares unfavorably to the reference voltage differential.

Abstract: Unlike a prior art digital predistortion compensation device for determining a compensation coefficient based on absolute value information about a baseband complex input signal, the present invention performs distortion compensation calculation in accordance with a complex coefficient polynomial using real and imaginary parts of the baseband complex input signal as its variables.

Abstract: A class D switching amplifier has a pulse width modulator that drives a speaker. The amplifier includes an over-current protection circuit, which includes current-monitoring MOSFETs that are each in parallel with one of four power MOSFETs. Signals taken from one side of the current-monitoring MOSFETs go to a logic circuit that removes the amplifier input circuit when the logic circuit indicates that an over-current condition is present. Current through the current-monitoring MOSFETs also goes through the speaker, thus improving amplifier efficiency.

Abstract: Subscriber line interface circuitry includes an integrated circuit having sense inputs for a sensed tip signal and a sensed ring signal of a subscriber loop. The integrated circuit generates a subscriber loop linefeed driver control signal in response to the sensed signals. The linefeed driver does not reside with the integrated circuit. A method for monitoring power dissipation of the linefeed driver components includes the step of sampling at least one of the tip and ring signals to determine a line voltage and a line current of a selected linefeed driver component. Instantaneous power dissipation of the linefeed component is estimated and then filtered to generate an estimated junction temperature of the linefeed component. In one embodiment, the linefeed driver includes a tip fuse series-coupled to the tip line and a ring fuse series-coupled to the ring line.

Abstract: Disclosed is an output overvoltage protection circuit for a power amplifier having a plurality of stages, which comprises a monitor circuit for monitoring an output overvoltage of an output transistor in the final stage of the power amplifier and allowing a current to flow therethrough in response to the monitored output overvoltage, and a current mirror circuit for supplying a current proportional to the current from the monitor circuit in such a manner that the base bias of the first-stage transistor of the power amplifier is reduced in response to the current supplied from the current mirror circuit, to reduce the output of the final-stage output transistor.

Abstract: A method and apparatus are provided for use with a power amplifier for protecting active devices on the power amplifier. A peak detector is used by control circuitry to detect the presence of a peak voltage that exceeds a threshold voltage. In response to the detection of a peak voltage, the gain of the power amplifier is reduced.

Abstract: A system and method of adjusting a sense amplifier includes providing an amplification control parameter to the sense amplifier. A temperature of the sense amplifier is monitored and the amplification control parameter to the sense amplifier is adjusted according to the temperature of the sense amplifier.

Abstract: A method and apparatus are disclosed for inferring amplifier load current from an internal control voltage governing a reference voltage in a multi-reference amplifier. Multi-reference amplifiers typically use internally-regulated references for application to the output stage. In that the output devices of these regulators exhibit limited gain or transconductance, internal voltage variances can be observed as a function of reference load current. This invention solves such problem at negligible additional cost.

Abstract: The present invention relates amplifiers using metal oxide semiconductor based integrated circuits. The present invention is particularly but not exclusively related to audio application mixed signal chips. The present invention provides an analog circuit for processing analog signals in an integrated circuit comprising a number of metal oxide semiconductor transistor devices, the circuit stage comprising a first said transistor device having a first oxide thickness, and a second said transistor device having a second and different oxide thickness. Preferably a cascode based op amp structure is implemented.

Abstract: A power amplifier includes an input transistor, an output transistor, and circuitry. The input transistor includes an input, a first node, and a second node, wherein the second node of the input transistor is coupled to a supply voltage return and the input of the input transistor operably coupled to receive an outbound radio frequency (RF) signal. The output transistor includes an input, a first node, and a second node, wherein the first node of the output transistor is coupled to provide an output of the power amplifier, the second node of the output transistor is coupled to the first node of the input transistor.

Abstract: An amplifier 2c amplifies a transmit signal and outputs the amplified transmit signal to an antenna 10. A drive current for driving the amplifier 2c is inputted to a drive current input terminal 7. A current divider circuit 41 is provided between the drive current input terminal 7 and the amplifier 2c, and divides the drive current among a plurality of paths. The current divider circuit 41 includes a plurality of switching elements provided in the paths, respectively, and switched between a conduction state and a blocking state; and a resistance element 13 provided in at least one of the plurality of paths. A detection section 5 detects an electrical parameter in the resistance element. A control section 6 switches the plurality of switching elements between a conduction state and a blocking state, based on the electrical parameter detected by the detection section 5.

Abstract: An overcurrent protection circuit for a power transistor includes a transconductance amplifier and a bias current circuit. The transconductance amplifier receives a first signal indicative of the magnitude of the load current conducted by the power transistor and a reference voltage and provides a second signal for controlling the load current. The transconductance amplifier further provides a third signal having a first logical state indicating normal operation and a second logical state indicating an overcurrent condition at the power transistor. The bias current circuit provides an output bias current to the transconductance amplifier in response to the third signal where the output bias current has a nominal current value in normal operation and an increased current value in an overcurrent condition. In this manner, a boost current is provided to the transconductance amplifier to increase the current limit response time when an overcurrent condition is detected.

Abstract: An audio amplifier system includes two amplifiers that are configured to drive loads through either DC or AC coupling. A third amplifier provides an AC ground return when the system is configured in the DC coupled mode, and is disabled when the system is configured in the AC coupled mode. A bypass circuit charges a bypass capacitor to provide a reference voltage level for the amplifiers. A mode detection circuit monitors the reference voltage level and the output of the third amplifier to determine the current operating mode. The third amplifier is disabled when the reference voltage exceeds the output of the third amplifier or when a shutdown condition is activated, such that the third amplifier is protected from short circuit conditions. The charge and discharge times of the bypass capacitor relate to the detected operating mode minimize click and pop in the amplified signals.

Abstract: An upstream amplifier is integrated on a substrate with a digital-to-analog converter (DAC) to form an integrated circuit. In an embodiment, a low-pass filter is also integrated on the substrate. The output signal level of the upstream amplifier is controllable. In embodiments, fine adjustments are made to the output signal level of the upstream amplifier by varying a bias current of the DAC. A software control bit is used to switch between a power-on mode of operation and a power-down mode of operation. The upstream amplifier transmits in a burst mode. The power consumption of the upstream amplifier scales with the amplifier's output signal level. A high degree of matching is attained between the positive and negative paths of the upstream amplifier. This provides high immunity from common-mode disturbances such as substrate noise, clock spurs, and glitches caused by a gain change.