Switched-current memory circuits for high-precision applications

We discuss circuit parameters that limit the precision of basic dynamic current-memory cells. In addition to analyzing current-copying errors caused by the finite output conductances of the current sources and by the clock-feedthrough (CFT) of the feedback switches, we analyze the noise performance of the basic memory cell. To reduce CFT and noise, we propose a novel circuit based on Miller capacitance-enhancement. Measurement results of memory cells integrated in a 1-μm CMOS process confirm the theoretical findings; with our CFT and noise reduction technique based on Miller enhanced capacitance and dummy switches, we achieve a dynamic range of 11 b at clock frequencies greater than 100 kHz     

An analog trimming circuit based on a floating-gate device

The application of floating-gate elements as adjustable components in analog CMOS circuits such as amplifiers is proposed. A simple trimming circuit based on this principle and delivering a differential current is described. Experimental results of a differential difference amplifier (DDA) containing two such circuits are given. After trimming, an offset voltage of 10 μV and a nonlinearity of 0.1% are achieved. Other analog circuits based on floating-gate elements like adjustable voltage sources and transconductances have been realized. Because they can be electrically reprogrammed, a wide range of applications, for example in neural nets, are possible     

CMOS current Schmitt trigger with fully adjustable hysteresis

A CMOS current Schmitt trigger whose hysteresis is independent of process parameters, transistor dimensions and power supplies is described. The hysteresis is determined by two currents and is adjustable over the range of the input current. The circuit function can be extended to a two-input current comparator with adjustable hysteresis.<>     

Design and Construction of a Pulsed Ultrasonic Air Flowmeter

The construction and specific function of a new ultrasonic flowmeter are described. The mean velocity of the respiratory air flow is calculated by measuring the transit times of short ultrasonic pulse-trains simultaneously transmitted upstream and downstream at a 650 Hz rate. The flowmeter system consists of a control unit and a separate flowhead. The former includes the power supplies, a controlling microprocessor, most of the signal processing circuitry, and three analog outputs for flow, volume, and temperature, respectively. The flowhead contains the respiratory tube with a constant circular cross section (length 90 mm, diameter 20 mm, dead space 35 cm3), a fast temperature sensor, two electronic circuits for processing of flow and temperature data, and a sound transmission channel with two capacitive ultrasonic wide-band transducers. This respiratory air flowmeter is extremely fast (response time 1-2 ms) and accurate, with low noise (below 9ml/s), with a wide flow range (bidirectional from 0 to 9 l/s) and with a linear frequency response up to 70 Hz.