Each hidden layer neuron in a multi-layer perceptron neural network comprises of synaptic weights, an adder and an activation function. The number of synaptic weights required per neuron is application specific and our contribution is a neuron implementation which is tailored to suit utilization in the complex baseband predistortion of a class-AB power amplifier given a wideband stimulus. The wideband or dynamic nature of the input calls for a neuron with ten synaptic weights as obtained through behavioral training and measurement. The performance of our neuron implementation is verified by measuring gain control, linearity, and bandwidth of the synaptic weights as well as the non-linear activation function. Finally a comparison with previously implemented neurons (both analog and digital) in terms of bandwidth, power consumption and linearity is done.

A 1-bit digital frequency tuning technique for continuous-time filter is presented. Unstable sigma-delta modulation is used. A 1-bit digital tuning signal can be generated by detecting the stability of a highly unstable sigma-delta modulation loop. Simulations on a third-order and a fourth-order sigma-delta modulation loops show up to 2% tuning accuracy that can be reached with the 1-bit tuning technique.

A novel biquad circuit is presented that allows the loop filter of a high-order continuous-time sigma-delta modulator to be implemented by cascading low-order biquad sections, considerably easing the design and implementation of the high-order continuous-time sigma-delta modulator. Experiment on a 4th-order bandpass continuous-time sigma-delta modulator is conducted successfully and the results are presented.

A direct-sequence spread-spectrum multiple-access (DS SSMA) system was examined, realized (hardware), and tested. Essentially, two transmitters were built: one had voice capability, whereas the other transmitted only binary data. Gold codes were used for the spreading sequence. The PN synchronization used a serial search technique for acquisition, and a tau-dither loop for tracking. A squaring loop and a differential encoding scheme (for carrier phase ambiguity) was used in the demodulation process, which was followed by conversion to a voice output when desired. The system was found to perform quite well under both single and multiple-access conditions. As a demonstration of the feasibility of implementing the system on chips, a few small blocks were put on ICs using CMOS technology. These performed as expected, and clearly demonstrated both the feasibility and attractiveness of a VLSI implementation.>