Abstract: In one embodiment, a switching regulator includes a first switching regulator stage configured between an input voltage and a first reference voltage and a second switching regulator stage configured between the first reference voltage and a second reference voltage. A first terminal of an inductor is coupled to an output of the first switching regulator stage and an output of the second switching regulator stage. The first switching regulator stage operates to produce an output voltage when the output voltage is configured above the first reference voltage, and the second switching regulator stage operates to produce an output voltage when the output voltage is configured below the first reference voltage.

Abstract: Techniques for efficiently generating a variable boosted supply voltage for an amplifier and/or other circuits are disclosed. In an exemplary design, an apparatus includes an amplifier, a boost converter, and a boost controller. The amplifier receives an envelope signal and a variable boosted supply voltage and provides an output voltage and an output current. The boost converter receives a power supply voltage and at least one signal determined based on the envelope signal and generates the variable boosted supply voltage based on the power supply voltage and the at least one signal. The boost controller generates the at least one signal (e.g., an enable signal and/or a threshold voltage) for the boost converter based on the envelope signal and/or the output voltage. The boost converter is enabled or disabled based on the enable signal and generates the variable boosted supply voltage based on the power supply voltage and the threshold voltage.

Abstract: In one embodiment, a switching regulator includes a first switching regulator stage configured between an input voltage and a first reference voltage and a second switching regulator stage configured between the first reference voltage and a second reference voltage. A first terminal of an inductor is coupled to an output of the first switching regulator stage and an output of the second switching regulator stage. The first switching regulator stage operates to produce an output voltage when the output voltage is configured above the first reference voltage, and the second switching regulator stage operates to produce an output voltage when the output voltage is configured below the first reference voltage.

Abstract: Apparatus and method for generating a DC pixel voltage are disclosed. The apparatus includes an amplifier configured to amplify an input signal to generate a voltage signal, wherein the input signal is generated in response to an ultrasonic wave reflecting off an item-to-be-imaged and propagating via a piezoelectric layer; a noise reduction circuit configured to pass the voltage signal from an output of the amplifier to a node, while reducing a propagation of noise from the output of the amplifier to the node; and a circuit configured to generate a DC pixel voltage based on the reduced-noise voltage signal.

Abstract: An apparatus, such as a pixel sensor for an ultrasonic imaging apparatus, is disclosed. The apparatus includes a first metallization layer coupled to a piezoelectric layer, wherein a first voltage is formed at the first metallization layer in response to an ultrasonic wave reflecting off an item-to-be-imaged (e.g., a user's fingerprint) and propagating through the piezoelectric layer, and wherein the first metallization layer is situated above a substrate; a second metallization layer situated between the first metallization layer and the substrate; and a device configured to apply a second voltage to the second metallization layer to reduce a parasitic capacitance between the first metallization layer and the substrate.

Abstract: Techniques for dynamically generating a headroom voltage for an envelope tracking system. In an aspect, an initial headroom voltage is updated when a signal from a power amplifier (PA) indicates that the PA headroom is insufficient. The initial headroom voltage may be updated to an operating headroom voltage that includes the initial voltage plus a deficiency voltage plus a margin. In this manner, the operating headroom voltage may be dynamically selected to minimize power consumption while still ensuring that the PA is linear. In a further aspect, a specific exemplary embodiment of a headroom voltage generator using a counter is described.

Abstract: Techniques for providing negative current information to a control loop for a buck converter in reverse boost mode. In an aspect, negative as well as positive current through an inductor is sensed and provided to adjust a ramp voltage in the control loop for the buck converter. The techniques may prevent current through the inductor during reverse boost mode from becoming increasingly negative without bound; the techniques thereby reduce settling times when the target output voltage is reduced from a first level to a second level. In an aspect, the negative current sensing may be provided by sensing negative current through a charging, or PMOS, switch of the buck converter. The sensed negative current may be subtracted from a current used to generate the ramp voltage.

Abstract: The present disclosure includes envelope tracking circuits and methods with adaptive switching frequency. In one embodiment, a circuit comprising an amplifier to receive an envelope tracking signal having an envelope tracking frequency and output voltage and current to a power supply terminal of a power amplifier circuit. A programmable comparator receives an output signal from the amplifier and generates a switching signal having a switching frequency. A switching regulator stage receives the switching signal and outputs a switching current to the power supply terminal. A frequency comparison circuit configures the programmable comparator based on the envelope tracking frequency and the switching frequency so that the switching frequency tracks the envelope tracking frequency.

Abstract: Techniques for generating a boost clock signal for a boost converter from a buck converter clock signal, wherein the boost clock signal has a limited frequency range. In an aspect, the boost clock signal has a maximum frequency determined by Vbst/T, wherein Vbst represents the difference between a target output voltage and a battery voltage, and T represents a predetermined cycle duration. The boost converter may include a pulse insertion block to limit the minimum frequency of the boost clock signal, and a dynamic blanking/delay block to limit the maximum frequency of the boost clock signal. Further techniques are disclosed for generally implementing the minimum frequency limiting and maximum frequency limiting blocks.

Abstract: Techniques for preventing reverse current in applications wherein a tracking supply voltage is placed in parallel with a switching power stage. The tracking supply voltage may be boosted to a level higher than a battery supply voltage using, e.g., a boost converter. In an aspect, a negative current detection block is provided to detect negative current flow from the boosted tracking supply voltage to the battery supply voltage. A high-side switch of the switching power stage may be disabled in response to detecting the negative current. To prevent false tripping, the tracking supply voltage may be further compared with the battery supply voltage, and a latch may be provided to further control the high-side switch.

Abstract: An oscillator includes an oscillating circuit having an input and an output configured to oscillate between a first state and a second state. The oscillating circuit includes a resistor-capacitor circuit configured to bias the oscillating circuit input towards a target voltage. The oscillating circuit is configured to transition the oscillating circuit output from the first state to the second state in response to the oscillating circuit input reaching a threshold voltage before it reaches the target voltage. Another oscillator includes an oscillating circuit having an input and an output configured to oscillate between the first state and the second state. The oscillating circuit is configured to transition the oscillating circuit output from the first state to the second state in response to the oscillating circuit input reaching a threshold voltage. A starting circuit is configured to set the oscillating circuit input to the threshold voltage to start the oscillating circuit.

Abstract: Simple and efficient techniques for closed loop control of a boost converter. In an aspect, a current feed-forward (CFF) mode of operation includes providing current information to a control logic block controlling transistor switches of the boost converter to advantageously smooth the signals present in the closed loop control of the system. In another aspect, a modified peak current (MPC) mode of operation includes providing a simplified control mechanism based on a peak current mode of operation. Both CFF mode and MPC mode may share similar circuit elements, allowing a single implementation to selectively implement either of these modes of control. Further techniques are provided for determining average current information for the logic block.

Abstract: Techniques for reducing ringing arising from L-C coupling in a boost converter circuit during a transition from a boost ON state to a boost OFF state. In an aspect, during an OFF state of the boost converter circuit, the size of the high-side switch coupling a boost inductor to the load is gradually increased over time. In this manner, the on-resistance of the high-side switch is decreased from a first value to a second (lower) value over time, which advantageously reduces ringing (due to high quality factor or Q) when initially entering the OFF state, while maintaining low conduction losses during the remainder of the OFF state. Further techniques are provided for implementing the high-side switch as a plurality of parallel-coupled transistors.

Abstract: Techniques for performing noise cancellation/attenuation are disclosed. In one design, an apparatus includes a power supply generator having a switcher, a coupling circuit, an envelope amplifier, and a feedback circuit. The switcher generates DC and low frequency components and the envelope amplifier generates high frequency components of a supply voltage for a load, e.g., a power amplifier. The switcher receives a first supply voltage and provides a switcher output signal having switcher noise. The coupling circuit receives the switcher output signal and provides a first output signal having a first version of the switcher noise. The feedback circuit receives the switcher output signal and provides a feedback signal. The envelope amplifier receives an envelope signal and the feedback signal and provides a second output signal having a second version of the switcher noise, which is used to attenuate the first version of the switcher noise at the load.

Abstract: Techniques for creating one or more notch frequencies in the power density spectrum of an output voltage generated by switching circuitry. In an aspect, high- and low-side switches are coupled to an output voltage via an inductor. The spectral power of the output voltage at one or more frequencies is estimated, and the estimated spectral power is provided to a switch controller controlling the switches. The switch controller may be configured to switch the switches only in response to detecting that the estimated spectral power at the notch frequency is at a minimum. In certain exemplary aspects, the techniques may be incorporated in an envelope-tracking system, wherein the switching circuitry forms part of a switched-mode power supply (SMPS) supplying low-frequency power to a power amplifier load.

Abstract: A method of operation of an ultrasonic sensor array includes receiving a receiver bias voltage at a receiver bias electrode of the ultrasonic sensor array to bias piezoelectric sensor elements of the ultrasonic sensor array. The method further includes receiving a transmitter control signal at the ultrasonic sensor array to cause an ultrasonic transmitter of the ultrasonic sensor array to generate an ultrasonic wave. The method further includes generating data samples based on a reflection of the ultrasonic wave. The receiver bias voltage and the transmitter control signal are received from an integrated circuit that is coupled to the ultrasonic sensor array.

Abstract: An apparatus includes an integrated circuit configured to be operatively coupled to a sensor array that is configured to generate an ultrasonic wave. The integrated circuit includes a transmitter circuit configured to provide a first signal to the sensor array. The integrated circuit further includes a receiver circuit configured to receive a second signal from the sensor array in response to providing the first signal. The sensor array includes an ultrasonic transmitter configured to generate the ultrasonic wave in response to the first signal and a piezoelectric receiver layer configured to detect a reflection of the ultrasonic wave.

Abstract: Techniques for dynamically generating a headroom voltage for an envelope tracking system. In an aspect, an initial headroom voltage is updated when a signal from a power amplifier (PA) indicates that the PA headroom is insufficient. The initial headroom voltage may be updated to an operating headroom voltage that includes the initial voltage plus a deficiency voltage plus a margin. In this manner, the operating headroom voltage may be dynamically selected to minimize power consumption while still ensuring that the PA is linear. In a further aspect, a specific exemplary embodiment of a headroom voltage generator using a counter is described.

Abstract: Techniques for efficiently generating a variable boosted supply voltage for an amplifier and/or other circuits are disclosed. In an exemplary design, an apparatus includes an amplifier, a boost converter, and a boost controller. The amplifier receives an envelope signal and a variable boosted supply voltage and provides an output voltage and an output current. The boost converter receives a power supply voltage and at least one signal determined based on the envelope signal and generates the variable boosted supply voltage based on the power supply voltage and the at least one signal. The boost controller generates the at least one signal (e.g., an enable signal and/or a threshold voltage) for the boost converter based on the envelope signal and/or the output voltage. The boost converter is enabled or disabled based on the enable signal and generates the variable boosted supply voltage based on the power supply voltage and the threshold voltage.

Abstract: An adaptive gate drive circuit that can generate a gate bias voltage with temperature compensation for a MOSFET is disclosed. The adaptive gate drive circuit may generate the gate bias voltage with variable drive capability to combat higher gate leakage current of the MOSFET at higher temperature. In one design, an apparatus includes a control circuit and a gate drive circuit. The control circuit generates at least one control signal having a variable frequency determined based on a sensed temperature of the MOSFET. For example, a clock divider ratio may be determined based on the sensed temperature of the MOSFET, an input clock signal may be divided based on the clock divider ratio to obtain a variable clock signal, and the control signal(s) may be generated based on the variable clock signal. The gate drive circuit generates a bias voltage for the MOSFET based on the control signal(s).