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DIRECT DIGITAL SYNTHESIS USING ANALOG EEPROM

IP.com Disclosure Number: IPCOM000006557D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2002-Jan-15
Document File: 2 page(s) / 97K

Publishing Venue

Motorola

Related People

Wayne P. Shepherd: AUTHOR [+2]

Abstract

Analog memory storage can replace the computa- storage for a phase accumulator resolution of 32 bits. tion of the output function and the digital to analog @AC) Amplitude quantization occurs as a result of the X bit blocks in a Direct Digital Synthesizer (DDS). The com- resolution of the DAC and the DAC non-linearities. putation of the sine function from the phase argument Replacing the computation and DAC blocks with ana- 6(n) is dilticult to pipeline and becomes a bottleneck in log memory significantly reduces the calculation inten- the maximum achievable system clock rate. To improve sity throughput limit and provides the flexibility for this the sine function is approximated (truncated) with additional output signal functions that do not have a corn- storage compression algorithms applied and a look up putation algorithm. In addition the phase and amplitude table is used over a fraction of a cycle. This results in quantization errors are a function of the analog memory phase quantization errors and creates spurious output read and write value resolution only. Figure 1, is an exam- noise. A straight forward implementation of the sine tic- ple of a direct digital synthesizer using phase computa- tion look-up table requires more than 4 Gsamples of tion and a DAC convertor.

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MOTOROLA INC. Technical Developments Volume 16 August 1992

DIRECT DIGITAL SYNTHESIS USING ANALOG EEPROM

by Wayne F! Shepherd and Bob Stengel

  Analog memory storage can replace the computa- storage for a phase accumulator resolution of 32 bits. tion of the output function and the digital to analog @AC) Amplitude quantization occurs as a result of the X bit blocks in a Direct Digital Synthesizer (DDS). The com- resolution of the DAC and the DAC non-linearities. putation of the sine function from the phase argument Replacing the computation and DAC blocks with ana- 6(n) is dilticult to pipeline and becomes a bottleneck in log memory significantly reduces the calculation inten- the maximum achievable system clock rate. To improve sity throughput limit and provides the flexibility for this the sine function is approximated (truncated) with additional output signal functions that do not have a corn- storage compression algorithms applied and a look up putation algorithm. In addition the phase and amplitude table is used over a fraction of a cycle. This results in quantization errors are a function of the analog memory phase quantization errors and creates spurious output read and write value resolution only. Figure 1, is an exam- noise. A straight forward implementation of the sine tic- ple of a direct digital synthesizer using phase computa- tion look-up table requires more than 4 Gsamples of tion and a DAC convertor.

Frequency

              Computation 2-J +(n) s -35 ' & +

EO s L s

?T

sin(ZYy) T

$E- "$2~

xl

Figure 1. Tiemey er al. architecture for DDFS.

  Analog memory has been demonstrated in at least two products available on the market today. Informa- tion Storage Devices solid state audio recorder/player ISD 1020 and Seiko's reference oscillator tuning adjust- ment. The technology is an EEPROM cell where an analog voltage is stored without ADC or DAC signal processing required. The analog EEPROM would be loaded during initialization with the si...