Carl M. Panasik

A 32 tap digitally controlled programmable transversal filter

A digitally controlled programmable transversal filter (DCPTF) has been developed that uses a 32-tap LiNbO/sub 3/ delay line and two LSI GaAs ICs to digitally control tap weight magnitude and sign. Compared to previously reported PTR devices, this third-generation device is significantly reduced in size and power, yet retains state-of-the-art performance. The device is completely programmable, constrained only by the bandwidth (100 MHz centered at 100 MHz) and the number of taps. The DCPTF is designed in 16-tap blocks to easily expand the number of taps. A calibration method is presented which removes nonideal GaAs FET (field-effect transistor) array gain states due to process variations. The on/off ratio of each individual tap is greater than 35 dB. The DCPTF is demonstrated as a bandpass filter with programmable center frequency and bandwidth.<<ETX>>

A 16 Tap Hybrid Programmable Transversal Filter Using Monolithic GaAs Dual-Gate FET Array

A hybrid programmable transversal filter (HPTF) is described that employs a LiNbO/sub 3/ SAW delay line and two monolithic dual-gate GaAs FET arrays to control magnitude and sign of the 16 tap weights. The HPTF is completely programmable and is constrained only by the bandwidth (100 MHz centered at 250 MHz) and the number of taps. Theoretical calculations of tap weight control range and dynamic range are presented, compared with experiment and used to justify the hybrid LiNbO/sub 3/ SAW - GaAs FET combination. A dynamic range of 85 dB and a continuously variable tap weight control range of 70 dB are demonstrated.

A 32 tap digitally controlled programmable transversal filter using LSI GaAs ICs (and SAW delay line)

A digitally controlled programmable transversal filter (DCPTF) is described that uses a LiNbO/sub 3/ surface-acoustic-wave (SAW) delay line and two GaAs large-scale-integrated (LSI) circuits to control magnitude and sign of the 32 tap weights. A radio-frequency (RF) signal is applied to an input transducer, which generates a surface acoustic wave that propagates down the LiNbO/sub 3/ substrate to an array of output electrodes. Each output electrode detects the electrical signal associated with the acoustic wave. Because of the delay between output electrodes, each electric signal is a delayed copy of the original output. The signal then flows into the RF tap-weighting-amplifier input. The amplifier outputs of each phase are connected to their respective summing buses. Negative tap weights are generated with an external 180 degrees hybrid. The DCPTF constitutes a significant reduction in size over previously reported PTFs with little sacrifice in performance. The filter is completely programmable and is constrained only by the bandwidth (100 MHz centered at 300 MHz) and the number of taps.<<ETX>>

Programmable transversal filter based adaptive line enhancer

A programmable transversal filter (PTF)-based adaptive line enhancer (ALE) subsystem is described. It covers the 30 to 58-MHz frequency range. The PTF-ALE can be utilized with frequency-hopping radio receivers to greatly reduce unwanted RF interference via a quickly programmable null. A subsystem configuration (adaptive line enhancer) and adaptive algorithm (differential steepest descent) are selected. A digitally controlled (TTL) PTF programmed by a standard personal computer with an off-the-shelf direct memory access interface is described. The PTF device has the capability to be reprogrammed at 3 mu sec per tap weight plan. The ALE subsystem consists of a delayed, unity gain channel and a difference channel containing the PTF. The subsystem creates a 40-dB single null, software programmable to any frequency in the range 30 to 58 MHz. The null has a 3-dB bandwidth of 45 KHz. When combined with a fast microprocessor, the PTF-ALF is ideal for excision of narrowband interfering signals in fast hopping communication systems.<<ETX>>

Site Survey for Wireless Communications Evaluation for New York Mercantile Exchange

The New York Mercantile Exchange (NYMEX) asked Texas Instruments (TI) to study and propose the implementation of a system to support commodities traders in the exchange trading pits. The system includes a custom hand held computer, an integrated wireless communications system, a wireless-to-wired network bridge, and a fault detection and recovery scheme. This paper summarizes the findings of a site survey on the trading floor at NYMEX both during off hours (“empty room” but with existing equipment) and during trading (hundreds of traders in constant motion present). The goal was to evaluate the system sensitivity and impact of the impairments in terms of friendly and external interferers. Using a spectrum analyzer and a tracking generator, we measured the real-time path loss and frequency response from the temporary access point to the hand-held computer. Measurements of the indoor propagation path loss at NYMEX show good correlation with theory. Due to the large number of metal structures and plasma displays there is significant multi-path throughout the room and, hence, very little shadowing. With a location 100 floors below the World Trade Center broadcast center, the NYMEX commodities floor is a particularly interesting environment from an external interferer standpoint (i.e. intermodulation suppression, adjacent channel rejection). In addition, the excessive trader activity and user density in a hyper-active physical environment places several constraints on communication system design.