Dynamic Offset Compensation Research Articles

Frequency-Based Sensor Interface with Dynamic Offset Compensation

Sensor interfaces need to be robust and accurate for many applications. This is more challenging for sensor systems operating in radiation environments because the mismatch between components grows as a result of the absorbed total ionizing dose (TID). In frequency-based sensor interfaces, the frequency drift of the voltage-controlled oscillator (VCO) can create dynamic output offset, gain, and linearity errors unless a calibration algorithm is included. In this paper, a digital intensive dynamic offset cancelation technique is proposed for an open loop VCO-based sensor to digital converter, which is achieved by making periodic adjustments to the average center biasing voltage of one of the VCOs in a differential architecture, in effect to make their center frequencies match. A simulation of the behavioral model of the proposed architecture was developed and hardware implementation of the whole system was performed on an FPGA by emulating, with digital modules, the characteristics of the two VCO outputs modulated with differential inputs. The results showed that the output offset error was reduced from around 5% to 0.1% for a relative oscillators’ drift close to 10% of the tuning range, and the SNDR is relatively maintained when subjected to variable relative VCO drifts.

A 15-Channel Orthogonal Code Chopping Instrumentation Amplifier for Area-Efficient, Low-Mismatch Bio-Signal Acquisition

This article presents a 15-channel orthogonal code chopping instrumentation amplifier (OCCIA) for an area-efficient and low gain-mismatch multi-channel bio-signal acquisition. Orthogonal codes directly modulate each channel and merge into a single signal for sharing IA, while performing dynamic offset compensation with low power consumption. Digitization-before-demodulation (DBD) transmits the combined modulated data directly, which alleviates ripple noise, and completely removes the demodulation and TX encoding overhead from the ASIC. The proposed OCCIA in 0.18-μm 1P6M CMOS, when compared with the recent multi-channel instrumentation amplifiers (IAs), shows the smallest area (0.019 mm 2 /Ch.), low gain mismatch (0.43%), with the lowest power consumption (1.97 μW/Ch.) and low crosstalk (<; -51.5 dB) at 490-Hz bandwidth.

Cryogenic Integrated Offset Compensation for Time Domain SQUID Multiplexing

Superconducting QUantum Interference Device (SQUID) multiplexing is a common technique in the use of large arrays of Transition Edge Sensors (TES). A Time Domain Multiplexer (TDM) combines input TES signals into one output signal using several SQUIDs. Different TES, SQUID and amplifier characteristics induce unavoidable different offsets on the multiplexed signal. Additionally, given the periodicity of the SQUID characteristic, the Flux Locked Loop (FLL) operating point is only defined modulo Φ 0. This can lead to a large output offset. In multiplexed mode, the difference between offsets associated with different pixels can induce a parasitic signal which is often larger than that of the TES. These offset signals drastically constrain the readout dynamic range and thus the maximum gain allowed. They also limit the signal-to-noise ratio, the FLL stability and the multiplexing frequency. Offsets in SQUID readout are discussed and offset compensation for TDM is presented. The dynamic calibration and compensation on a simplified 4:1 TDM are demonstrated in simulation. Dynamic offset compensation is being implemented on a cryogenic SiGe integrated circuit operated at 4 K for 128:1 TDM.

Offset reduction in Hall devices by continuous spinning current method

A novel method for dynamic offset compensation in a Hall plate is presented. The continuous spinning current method is based on minimalsize four-contact Hall devices and, therefore, the lowest possible offset resulting from material inhomogeneities is achieved. A continuous spinning current vector is generated in the device by spatially superimposing two periodic biasing currents. The resulting voltages allow the constant Hall voltage to be separated from the periodic offset voltage. Remaining offsets are below 10 μT, which corresponds to fractions of the earth's magnetic field.