A fully configurable bias current reference is described. The output of the current reference is a gate voltage which produces a desired current. For each daisy-chained bias, 32 bits of configuration are divided into 22 bits of bias current, 6 bits of active-mirror buffer current, and 4 bits of other configuration. Configuration of each bias allows specifying the type of transistor (nfet or pfet), whether the bias is enabled or weakly pulled to the rail, whether the bias is for a cascode, and whether the bias transistor uses a shifted source (SS) voltage for sub-off-current biasing. In addition, the current reference integrates a pair of voltage regulators that generate stable voltage sources near the rails, suitable for the SS current references. Measurements from fabricated current references built in 180 nm CMOS show that the reference achieves at least 110 dB (22-bit) dynamic range and reaches 160dB when power-rail gate biasing is included. Generated bias currents reach at least 30x smaller current than the transistor off-current. ABSTRACT A fully configurable bias current reference is described. The output of the current reference is a gate voltage which produces a desired current. For each daisychained bias, 32 bits of configuration are divided into 22 bits of bias current, 6 bits of active-mirror buffer current, and 4 bits of other configuration. Configuration of each bias allows specifying the type of transistor (nfet or pfet), whether the bias is enabled or weakly pulled to the rail, whether the bias is for a cascode, and whether the bias transistor uses a shifted source (SS) voltage for sub-offcurrent biasing. In addition, the current reference integrates a pair of voltage regulators that generate stable voltage sources near the rails, suitable for the SS current references. Measurements from fabricated current references built in 180 nm CMOS show that the reference achieves at least 110 dB (22-bit) dynamic range and reaches 160dB when power-rail gate biasing is included. Generated bias currents reach at least 30x smaller current than the transistor off-current. Each current reference occupies an area of 620x50 um 2 . The design kit schematics and layout are open-sourced. 32-bit Configurable Bias Current Generator with Sub-Off-Current Capability

A linearly tunable low-voltage CMOS transconductor featuring a new adaptative-bias mechanism that considerably improves the stability of the processed-signal common-mode voltage over the tuning range, critical for very-low voltage applications, is introduced. It embeds a feedback loop that holds input devices on triode region while boosting the output resistance. Analysis of the integrator frequency response gives an insight into the location of secondary poles and zeros as function of design parameters. A third-order low-pass Cauer filter employing the proposed transconductor was designed and integrated on a 0.8m n-well CMOS standard process. For a 1.8-V supply, filter characterization revealed = 0.93 MHz, = 1.82 MHz, min = 44 08, dB, and max = 0 64 dB at nominal tuning. Tuned by a dc voltage TUNE , the filter bandwidth was linearly adjusted at a rate of 11.48 kHz/mV over nearly one frequency decade. A maximum 13-mV deviation on the common-mode voltage at the filter output was measured over the interval 25 mV TUNE 200 mV. For out = 300 mV pp and TUNE = 100 mV, THD was 55.4 dB. Noise spectral density was 0.84 V/Hz 1 2 @1 kHz and S/N = 41 dB @ out = 300 mV pp and 1-MHz bandwidth. Idle power consumption was 1.73 mW @ TUNE = 100 mV. A tradeoff between dynamic range, bandwidth, power consumption, and chip area has then been achieved. Index Terms-Common-mode stability, filter tuning,-, low-voltage CMOS filter. I. INTRODUCTION T HE REMARKABLE GROWTH in mobile and batterypowered systems has demanded continuous efforts on improving low-voltage (LV) signal-processing circuits [1]. The tradeoff between dynamic range, bandwidth, power consumption, and chip area minimization and, hence, production costs has become a difficult task on designing such circuits. LV filters can be employed where dynamic range is less strict, such as video and low-quality audio applications. Even though many transconductors reported to date meet LV requirements [2], [3], or could be reconfigured to (e.g., [4]-[6]), the dependence of the processed signal common-mode voltage on their tuning

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