Abstract: Apparatus and methods for amplifier input-overvoltage protection with low leakage current are provided herein. In certain embodiments, amplifier input circuitry for an amplifier includes a pair of input terminals, a pair of input transistors each having a control input (for instance, a transistor gate), a pair of protection transistors each connected between one of the input terminals and the control input of a corresponding one of the input transistors, and a bidirectional clamp connected between the control inputs of the input transistors. Implementing the amplifier input circuitry in this manner provides a number of advantages including, but not limited to, robust protection against input overvoltage and low input-leakage current.

Abstract: Apparatus and methods for reducing charge injection mismatch are provided herein. In certain implementations, an electronic circuit includes one or more switch banks. Each switch bank can include a selection circuit and a plurality of switches that can be controlled using one or more clock signals. The selection circuit can select a first portion of the switches for operation in a first switch group and a second portion of the switches for operation in a second switch group. During a calibration, the electronic circuit's charge injection mismatch can be directly or indirectly observed for different switch configurations of the switch banks. The electronic circuit can be programmed to operate with the selected switch configurations of the switch banks to provide the electronic circuit with small charge injection mismatch.

Abstract: Embodiments of the present disclosure provide mechanisms for measuring currents flowing in one or more conductor wires. The mechanisms are based on using magnetic sensor pairs arranged within a housing with an opening for the wires, where each magnetic sensor pair can generate a pair of signals indicative of magnetic fields in two different directions. The outputs of the sensor pairs can be used to derive a measure of current(s) flowing through the one or more wires. The use of magnetic sensor pairs that can measure magnetic field in two different directions may enable simultaneous current measurement in multiple wires placed within the opening, improve accuracy of current measurements while relaxing requirements for precise control of the placement of the wire(s), reduce the impact of stray magnetic interference, and enable both AC and DC measurements.

Abstract: Techniques to generate two separate temperature independent reference voltages. The reference voltages can be generated using a chain of ?VBE cells. A cross-quad ?VBE-cell-based bandgap voltage reference can cancel out noise of associated current sources by forcing them to correlate. Several ?VBE stages can be cascaded together to generate an appreciable PTAT component that can cancel the CTAT component from VBE. In some example configurations, only BJTs are used—without requiring use of an amplifier—to generate the bandgap voltages; in this way, extremely low noise voltage references can be generated. The PTAT and the CTAT voltages can be combined to generate a bandgap voltage of approximately VG0 or approximately 2VG0.

Abstract: Techniques to generate two separate temperature independent reference voltages. The reference voltages can be generated using a chain of ?VBE cells. A cross-quad ?VBE-cell-based bandgap voltage reference can cancel out noise of associated current sources by forcing them to correlate. Several ?VBE stages can be cascaded together to generate an appreciable PTAT component that can cancel the CTAT component from VBE. In some example configurations, only BJTs are used—without requiring use of an amplifier—to generate the bandgap voltages; in this way, extremely low noise voltage references can be generated. The PTAT and the CTAT voltages can be combined to generate a bandgap voltage of approximately VG0 or approximately 2VG0.

Abstract: Embodiments of the present disclosure provide mechanisms for measuring currents flowing in one or more conductor wires. The mechanisms are based on using magnetic sensor pairs arranged within a housing with an opening for the wires, where each magnetic sensor pair can generate a pair of signals indicative of magnetic fields in two different directions. The outputs of the sensor pairs can be used to derive a measure of current(s) flowing through the one or more wires. The use of magnetic sensor pairs that can measure magnetic field in two different directions may enable simultaneous current measurement in multiple wires placed within the opening, improve accuracy of current measurements while relaxing requirements for precise control of the placement of the wire(s), reduce the impact of stray magnetic interference, and enable both AC and DC measurements.

Abstract: A sigma-delta ADC circuit with an analog loop filter circuit can be multiplexed between different inputs by flushing the memory of the analog loop filter integrators and the digital decimation filter and filling it with new data for the current input. However, filling the memory can be slow with respect to the sampling frequency because the information about past history has to be built up before meaningful output data can be generated. Thus, the multiplexing rate between channels using a sigma-delta ADC circuit can be slowed by such memory flushing. A multiplexed sigma-delta ADC circuit is described that can overcome these problems so as to be able to support cycle-by-cycle sampling of multiple channels. These techniques can provide a fast sigma-delta analog-to-digital converter (ADC) circuit that is small in area and that can multiplex over a number of channels dynamically.

Abstract: An analog front end (AFE) system for substantially eliminating quantization error or noise can combine an input of an integrator circuit in the AFE system with an input of the digital-to-analog converter (DAC) circuit in the feedback loop of the AFE system. By combining the input of the integrator with the input of the DAC circuit in the feedback loop, the in-band quantization noise of the filter can be substantially eliminated, thereby improving measurement accuracy.

Abstract: An analog front end system can include a filter bypass switch connected in a boot-strapped configuration to pull a control terminal of the filter bypass switch above or below a supply voltage. Using bootstrapped switches can allow both the charge injection and capacitive coupling of the bypass switches of a differential anti-alias filter (AAF) to be common mode. A differential input signal of the ADC is not affected by the charge injection and capacitive coupling of the bypass switches in the AAF filter to a first order.

Abstract: A low power high precision mixed signal analog to digital converter is provided for processing biometric signals in the presence of a large interferer signal for cableless patient monitoring; a capacitive difference circuit produces an analog difference signal by differencing an analog feedback loop signal and an input signal; an analog-to-digital converter sigma delta converter produces a digital version of the difference signal, a digital feedback loop includes a digital integrator and a capacitive digital-to-analog converter configured to produce the analog loop feedback signal based upon the digital version of the difference.

Abstract: An analog front end system can include a filter bypass switch connected in a boot-strapped configuration to pull a control terminal of the filter bypass switch above or below a supply voltage. Using bootstrapped switches can allow both the charge injection and capacitive coupling of the bypass switches of a differential anti-alias filter (AAF) to be common mode. A differential input signal of the ADC is not affected by the charge injection and capacitive coupling of the bypass switches in the AAF filter to a first order.

Abstract: An analog front end (AFE) system for substantially eliminating quantization error or noise can combine an input of an integrator circuit in the AFE system with an input of the digital-to-analog converter (DAC) circuit in the feedback loop of the AFE system. By combining the input of the integrator with the input of the DAC circuit in the feedback loop, the in-band quantization noise of the filter can be substantially eliminated, thereby improving measurement accuracy.

Abstract: A low power high precision mixed signal analog to digital converter is provided for processing biometric signals in the presence of a large interferer signal for cableless patient monitoring; a capacitive difference circuit produces an analog difference signal by differencing an analog feedback loop signal and an input signal; an analog-to-digital converter sigma delta converter produces a digital version of the difference signal, a digital feedback loop includes a digital integrator and a capacitive digital-to-analog converter configured to produce the analog loop feedback signal based upon the digital version of the difference.

Abstract: Aspects of this disclosure relate to an amplifier with at least two chopper amplifier channels in parallel between a shared input and differential nodes. The amplifier can multiplex outputs of the chopper amplifier channels to provide the output of one or more chopper amplifier channels to the differential nodes at a time. In certain embodiments, this can mask dynamic settling errors.

Abstract: Aspects of this disclosure relate to an amplifier with at least two chopper amplifier channels in parallel between a shared input and differential nodes. The amplifier can multiplex outputs of the chopper amplifier channels to provide the output of one or more chopper amplifier channels to the differential nodes at a time. In certain embodiments, this can mask dynamic settling errors.

Abstract: An input stage to an analog to digital converter (ADC) includes at least one sampling capacitor (SC) for sampling an input signal in acquire phases, a capacitive gain amplifier (CGA) for providing the input signal to the SC, and bandwidth control means. The bandwidth control means is configured to ensure that the SC has a first bandwidth during a first part of an acquire phase and has a second bandwidth during a subsequent, second, part of said acquire phase, the second bandwidth being smaller than the first. In this manner, first, the input signal is sampled at a higher, first, bandwidth allowing to take advantage of using a high-bandwidth CGA to minimize settling error on the SC, and, next, during a second part of the same acquire phase, the input signal is sampled at a lower, second, bandwidth advantageously decreasing noise resulting from the use of a high-bandwidth CGA.

Abstract: Apparatus and methods for chopper amplifiers are provided herein. In certain configurations, a chopper amplifier includes at least one differential transistor bank including a selection circuit and a plurality of transistors. The selection circuit can select a first portion of the transistors for operation in a first transistor group and a second portion of the transistors for operation in a second transistor group. During calibration, the chopper amplifier's input offset can be observed for different transistor configurations of the differential transistor banks. Although the transistors of a particular bank can be designed to have about the same drive-strength and/or geometry, the chopper amplifier can have a different input offset in different transistor configurations due to manufacturing mismatch between transistors, such as process variation.

Abstract: Apparatus and methods for reducing charge injection mismatch are provided herein. In certain implementations, an electronic circuit includes one or more switch banks. Each switch bank can include a selection circuit and a plurality of switches that can be controlled using one or more clock signals. The selection circuit can select a first portion of the switches for operation in a first switch group and a second portion of the switches for operation in a second switch group. During a calibration, the electronic circuit's charge injection mismatch can be directly or indirectly observed for different switch configurations of the switch banks. The electronic circuit can be programmed to operate with the selected switch configurations of the switch banks to provide the electronic circuit with small charge injection mismatch.

Abstract: A voltage reference circuit comprises a plurality of ?VBE cells, each comprising four bipolar junction transistors (BJTs) connected in a cross-quad configuration and arranged to generate a ?VBE voltage. The plurality of ?VBE cells are stacked such that their ?VBE voltages are summed. A last stage is coupled to the summed ?VBE voltages and arranged to generate one or more VBE voltages which are summed with the ?VBE voltages to provide a reference voltage. This arrangement serves to cancel out first-order noise and mismatch associated with the two current sources present in each ?VBE cell, such that the voltage reference circuit provides ultra-low 1/f noise in the bandgap voltage output.

Abstract: Apparatus and methods for chopper amplifiers are provided herein. In certain configurations, a chopper amplifier includes at least one differential transistor bank including a selection circuit and a plurality of transistors. The selection circuit can select a first portion of the transistors for operation in a first transistor group and a second portion of the transistors for operation in a second transistor group. During calibration, the chopper amplifier's input offset can be observed for different transistor configurations of the differential transistor banks. Although the transistors of a particular bank can be designed to have about the same drive-strength and/or geometry, the chopper amplifier can have a different input offset in different transistor configurations due to manufacturing mismatch between transistors, such as process variation.