Very wide range tunable CMOS/bipolar current mirrors with voltage clamped input

In low power current mode signal processing circuits it is often necessary to use current mirrors to replicate and amplify/attenuate current signals and clamp the voltage of nodes with high parasitic capacitances so that the smallest currents do not introduce unacceptable delays. The use of tunable active-input current mirrors would meet both requirements. In conventional active-input current mirrors, stability compensation is required. Furthermore, once stabilized, the input current cannot be made arbitrarily small. In this paper we introduce two new active-input current mirrors that clamp their input node to a given voltage. One of them does not require compensation, while the other may under some circumstances. However, for both, the input current may take any value. The mirrors can operate with their transistors biased in strong inversion, weak inversion, or even as CMOS compatible lateral bipolar devices. If it is biased in weak inversion or as lateral bipolars, the current mirror gain can be tuned over a very wide range. According to the experimental measurements provided in this paper, the input current may spawn beyond nine decades and the current mirror gain can be tuned over 11 decades. As an application example, a sinusoidal gm-C-based VCO has been fabricated, whose oscillation frequency could be tuned for over seven decades, between 74 mHz and 1 MHz.Office of Naval Research (USA) N00014-95-1-040

Accurate Settling-Time Modeling and Design Procedures for Two-Stage Miller-Compensated Amplifiers for Switched-Capacitor Circuits

We present modeling techniques for accurate estimation of settling errors in switched-capacitor (SC) circuits built with Miller-compensated operational transconductance amplifiers (OTAs). One distinctive feature of the proposal is the computation of the impact of signal levels (on both the model parameters and the model structure) as they change during transient evolution. This is achieved by using an event-driven behavioral approach that combines small- and large-signal behavioral descriptions and keeps track of the amplifier state after each clock phase. Also, SC circuits are modeled under closed-loop conditions to guarantee that the results remain close to those obtained by electrical simulation of the actual circuits. Based on these models, which can be regarded as intermediate between the more established small-signal approach and full-fledged simulations, design procedures for dimensioning SC building blocks are presented whose targets are system-level specifications (such as ENOB and SNDR) instead of OTA specifications. The proposed techniques allow to complete top-down model-based designs with 0.3-b accuracy.Ministerio de Educación y Ciencia TEC2006-03022Junta de Andalucía TIC-0281

Adaptive Neural Coding Dependent on the Time-Varying Statistics of the Somatic Input Current

It is generally assumed that nerve cells optimize their performance to reflect the statistics of their input. Electronic circuit analogs of neurons require similar methods of self-optimization for stable and autonomous operation. We here describe and demonstrate a biologically plausible adaptive algorithm that enables a neuron to adapt the current threshold and the slope (or gain) of its current-frequency relationship to match the mean (or dc offset) and variance (or dynamic range or contrast) of the time-varying somatic input current. The adaptation algorithm estimates the somatic current signal from the spike train by way of the intracellular somatic calcium concentration, thereby continuously adjusting the neuronś firing dynamics. This principle is shown to work in an analog VLSI-designed silicon neuron

34th Midwest Symposium on Circuits and Systems-Final Program

Organized by the Naval Postgraduate School Monterey California. Cosponsored by the IEEE Circuits and Systems Society. Symposium Organizing Committee: General Chairman-Sherif Michael, Technical Program-Roberto Cristi, Publications-Michael Soderstrand, Special Sessions- Charles W. Therrien, Publicity: Jeffrey Burl, Finance: Ralph Hippenstiel, and Local Arrangements: Barbara Cristi