Ernest Stern

A SAW/CCD programmable matched filter

A charge‐coupled device (CCD) has been integrated with a surface‐acoustic‐wave (SAW) piezoelectric delay line in a hybrid gap‐coupled structure to produce an electronically programmable analog matched filter in which the filter function is controlled by the charge pattern clocked into the CCD. This device allows analog‐analog correlation of SAW input signals of ≲40‐MHz bandwidth and ≲3.5‐μs duration. Programming time is 6 ms at a 100‐kHz clock rate, and the reference holding time is 1 s for a 3‐dB degradation of the correlation peak. Operation as a matched filter for a 3.25‐μs‐long 13‐bit Barker‐encoded signal yields a peak correlation level of −41 dB m.

A SAW/CCD accumulating correlator

A new analog‐signal‐processing device is reported in which a charge‐coupled device (CCD) is coupled to a piezoelectric surface acoustic wave (SAW) delay line across a 300‐nm gap. The CCD samples multiply, accumulate, and read out the cross‐correlation function of two wide‐band SAW input signals which counterpropagate on the delay line. A signal‐processing gain of 30 dB at a bandwidth of 20 MHz has been observed by correlating biphase modulated pseudonoise waveforms of 100‐μs duration in the presence of Gaussian noise. This compact hybrid structure provides 300 discrete samples of a 7‐μs segment of the correlation function.

An acoustic SAW/CCD buffer memory device

A SAW piezoelectric delay line has been integrated with a silicon charge‐coupled shift register device (CCD) across a 300‐nm gap to produce a fast‐in slow‐out buffer memory. A prototype with an input bandwidth of 40 MHz centered around 107 MHz, an input signal duration time of 3.5 μs, and an output clock rate of 100 kHz has been fabricated and tested. The basic configuration of this SAW/CCD consists of a lithium niobate (LiNbO3) delay line, in close proximity to an array of 300 sampling fingers connected to a 300‐stage buried‐channel CCD on a p‐type silicon susbtrate. The output of the CCD retains both amplitude and phase of the input signal.

A CCD-Programmable SAW Matched Filter

A charge-coupled device (CCD) has been integrated with a SAW delay line to produce an electronically programable analog matched filter in which the filter function is controlled by the charge pattern clocked into the CCO. A prototype with an input signal bandwidth of 40 MHz centered around 107 MHz, a correlation time of 3.5 us and an analog input reference clock rate of 100 kHz has been fabricated and tested. This device consists of a LiNb03 delay line coupled across a gap to a silicon substrate. An output e lectrode on the LiNb03 is capacitively coupled to an array of 300 conducting fingers connected to a 300-stage CCD shift register on the silicon substrate. Nonlinearities in the silicon multiply the RF fields accompanying a SAW signal with dc potentials programed on the f ingers by the CCD, and the local product terms are summed on the o utput electrode to produce the d esired cross-corrdation between reference and signal waveforms. Operation as a matched filter for a 3.25-us-long 13-bit Barker-encoded signal yields a peak correlation level of -41 dBm.

Four-Wave Interactions in Acoustoelectric Integrating Correlators

Device Structure Four-wave acoustoelectric interactions have been observed in an integrating correlator device. use of the four-wave process provides both signifi- cantly improved device performance over that achieved with three-wave interactions and makes possible a unique signal-processing function: triple-product c orrelation. These electric-field interactions involve the differential delay, mixing, and time-integration of two surface acoustic waves (SAWs) at frequencies w1 and 9 counter- propagating on a LiNb03 delay line in the presence of a uniform pump at a frequency w1 + w2 applied to a PtSi diode array. A narrow (%350-nm) air gap provides coupling of the array to the evanescent RF fields accompanying the SAWs. Nonlinearities in the silicon provide local mixing of the three input RF fields to create a quasi-static field of finite wavevector. Time-integration of this field produces a stationary wave of charge which is stored in the diode array. A similar four-wave process is used to scan this charge pattern. The two interactions have been cascaded to demonstrate the correlation of a waveform with a time-bandwidth product in excess of 10,000.

A SAW Accumulating Correlator with CCD Readout

An accumulating correlator is described in which the multiplication and time-integration of many samples of two wideband surface acoustic wave (SAW) inputs are achieved in a charge-coupled device (CCD). The CCD is coupled to a LiNb03 delay line across a 350-nm gap by means of an array of 300 polysilicon taps. The SAW inputs counterpropagate on the delay line, and the cross-correlatio n is subsequently r eadout f rom the CCD. Electric fields accompanying the signal and reference SAWS are picked up by the taps, mixed by nonlinearities in the silicon substrate, and the dc mixing products are accumulated in the CCD; thus the charge in each well represents a discrete sample of the correlation between signal and reference. The spatial charge pattern is read out from the CCD to provide 300 discrete samples of a 7-LIS segment of the c orrelation function. T his unique SAW/CCD structure has produced a signal-processin g gain of 30 dB at a bandwidth of 20 MHz for a biphase-encoded waveform dominated by Gaussian noise; and it combines in a single device a number of significant advantages, These include analog-analog correlation, programmability, wide input bandwidth, selectable output data rate, and compactness.

Four‐wave interactions in acoustoelectric integrating correlators

Four‐wave acoustoelectric interactions have been observed in an integrating correlator which provide both significantly improved device performance over that achieved with three‐wave interactions and make possible a unique signal‐processing function: triple‐product correlation. These interactions involve the differential delay, mixing, and time integration of two (ω1, ω2) surface acoustic waves (SAW’s) counterpropagating on a LiNbO3 delay line in the presence of a uniform (ω3=ω1+ω2) pump applied to a PtSi diode array and a stationary wave of charge stored in the diode array. A narrow (∼350 nm) air gap provides coupling of the array to the evanescent rf fields accompanying the SAW’s; thus, the silicon nonlinearities provide local mixing of the three rf fields and a fourth field, at dc, which accompanies the stored charge pattern. Two four‐wave interactions have been cascaded (the first creates the stored charge, the second scans the charge pattern) to demonstrate the correlation of a waveform with a time‐b...

Performance Requirements For Analog Signal Processors In Radar And Communications Systems

MIT Lincoln Laboratory is perfecting surface-acoustic-wave, acoustoelectric and charge-coupled devices which perform the functions of correlation and Fourier transformation and meet the requirements for radar and communication systems. Examples will be given of the performance limitations of acoustoelectric convolvers and memory-correlators, of chirp-transform devices, and of programmable CCD matched filters. A critical evaluation of the suitability of these components for system applications will be given.