Martijn F. Snoeij

Multiple-Ramp Column-Parallel ADC Architectures for CMOS Image Sensors

This paper presents a CMOS imager with a column-parallel ADC architecture based on a multiple-ramp single-slope (MRSS) ADC. Like the well-known column-level single-slope ADC, an MRSS ADC uses a very simple analog column circuit, which mainly consists of an analog comparator and some switches. A prototype imager using the MRSS ADC architecture was realized in a 0.25 CMOS process. Measurements demonstrate that the conversion speed of an MRSS ADC is 3.3 higher than a single-slope ADC while dissipating only 16% more power. Furthermore, the MRSS ADC can be easily adapted to exhibit a companding characteristic, which exploits the amplitude-dependent nature of the photon shot noise present in imager signals. Measurements show that the resulting multiple-ramp multiple-slope ADC is 25% faster than an MRSS ADC while dissipating the same amount of power.

A 36 V Programmable Instrumentation Amplifier With Sub-20

A 36 V capable programmable gain instrumentation amplifier (PGA) is presented with sub-20 muV offset, sub-0.2 muV/degC offset drift and a common-mode rejection (CMRR) that exceeds 120 dB at all gain settings without any trimming. It is the first 36 V capable precision PGA implemented in a high-voltage CMOS process, which, in addition, incorporates several additional functions, such as the detection of input and output fault conditions, provisions for improving system-level settling time and an input switch network. All op-amps used in the PGA employ chopper stabilization with a notch filter that removes chopping glitches, leading to low offset and drift and no 1/f noise. The PGA has a total of 22 gain steps (binary steps between 1/8 to 128, each with an optional multiplying factor of 1 or 1.375) with better than 0.1% gain accuracy, < 0.001% nonlinearity and sub-2 ppm/C gain drift. The input switch network, in addition to acting as a 2-channel multiplexer, also enables various system-level diagnostic features. The PGA is implemented in a 0.35 mum CMOS process with a 36 V extension, has a 3.6 times 2.4 mm chip area and consumes a total quiescent current of 3 mA.

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This paper presents two integrated magnetic sensor ICs for isolated current measurement that have a fluxgate magnetometer co-integrated along with circuitry on a die. The integrated fluxgate has a sensitivity of 250 V/T and a 500 ksps readout circuit and requires only 5.4 mW for fluxgate excitation, which is 20x more power-efficient than the state of the art. The fluxgate magnetometer was used to realize the first fully integrated sensor IC for closed-loop current sensing. It achieves a dynamic range of 112 dB and a nonlinearity below 0.03%. A second realization provides a precision magnetic sensor IC that can be used for open-loop and differential-field current sensing. It features a sensor gain variation of 0.04% (1-sigma), a nonlinearity below 0.2%, a bandwidth of 47 kHz, and a dynamic range of 100 dB.

V Offset and a CMRR in Excess of 120 dB at All Gain Settings

This paper presents two integrated magnetic sensor ICs for isolated current sensing. Both employ an integrated fluxgate magnetometer with a sensitivity of 250V/T and a 500ksps readout circuit. Only 5.4mW is required to excite the sensor, which is 20x more power efficient than the state-of-the-art. With an external magnetic core, the resulting closed-loop current sensor IC achieves a dynamic range of 112dB and a non-linearity below 0.03%, while the open-loop current sensor IC has a dynamic range of 100dB and a non-linearity below 0.2%.

Integrated Fluxgate Magnetometer for Use in Isolated Current Sensing

A 36V JFET-input bipolar operational amplifier is presented with a maximum offset drift of 1μV/°C over a temperature range of −40 to 125°C, which represents a 3x improvement on the state-of-the-art. This is achieved with a drift-compensating circuit incorporated in the input stage that relies on a wafer-level 2-tem-perature laser-trimming method. The opamp has a GBW of 11MHz, a flat-band noise of 5.1nV/√Hz, a slew-rate of 20V/μs, a −126dB (0.00005%) total harmonic distortion plus noise (THD+N) ratio, and a quiescent current of 1.8mA. This combination of high slew rate and good noise-to-power ratio is accomplished through the use of a linearized class-AB boosting circuit in the input stage.

An integrated fluxgate magnetometer for use in closed-loop/open-loop isolated current sensing

Fluxgate sensors have typically only 100 μT range, which sometimes limits their applications. The main obstacle for increasing the measurement range is the power dissipated in their feedback coil. Until now, the feedback was always continuous. We suggest using pulse excitation only for the active part of the period, in which an output signal is present. In this paper, we show for the first time that if the sensor is excited by short pulses, the feedback need not be continuous, but it can be formed by the pulses slightly wider than the excitation pulses. We have shown that, in our case, the feedback current duty cycle can be only 17.25%. This means that for the same power, we can increase maximum feedback current and, thus, the range by the factor of three. We show that this can be done without compromising the sensor performance.

A 36V JFET-input bipolar operational amplifier with 1μV/°C maximum offset drift and −126dB total harmonic distortion

A 36 V programmable gain amplifier (PGA) is presented with sub -20 muV offset and CMRR exceeding 120 dB in all gains. It is the first 36 V capable precision PGA that is implemented in a high-voltage CMOS process, allowing for several important additional functions, such as the detection of input and output fault conditions and an input switch network. This switch network in addition to acting as a 2-channel multiplexer also allows for various system-level diagnostic features. All opamps used in the PGA use chopper stabilization with a notch filter that removes chopping glitches, leading to very low offset for all gains and low 1/f noise. The input referred offset voltage is below 20 muV (G=128). The PGA is implemented in a 0.35 um CMOS process with a 36 V extension, and has a total quiescent current of 2.7 mA.

Flugate Sensor With Pulse Feedback

A 36V precision voltage-to-current converter for 0–24mA loops is presented. It utilizes dynamic element matching (DEM) and an auto-calibration technique to achieve low DC inaccuracy (0.2%) and low DEM ripple (0.007%). Measurement results show that the auto-calibration suppresses the DEM ripple by a factor of 14, thus eliminating the need for a bulky off-chip ripple-suppression filter. The prototype chip is implemented in a 0.35μm CMOS process occupying 0.84mm2. It has a quiescent current of 0.5mA and a rise time of 10.2μs for a 1mA–23mA output step.