System, consisting of sample and hold digital-to-analog converter, clock circuit, sample delay circuit, initial condition circuit and interpolator circuit, improves accuracy of reconstructed analog signal without increasing sample rates

Dotson, W. P.

English

NASA Technical Reports Server

1972	 B72-10030 
NASA TECH BRIEF 
Manned Spacecraft Center
	
_4V 
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Third Order Digital-To-Analog Converter 
A digital-to-analog converter system, utilizing third 
order interpolation between sample points, improves the 
accuracy of the reconstructed analog signal without in-
creasing sample rates. 
The converter system consists of a sample and 
hold digital-to-analog converter, a clock circuit, a sample 
delay circuit, an initial condition circuit, and an inter-
polator circuit. The sample and hold digital-to-analog 
converter changes the pulse code modulated telemetry 
signal to a pulse amplitude modulated signal. The output 
of the converter feeds the sample delay circuit, which 
stores the four most recent data points. The data points 
are inputs for the initial condition circuitry, which cal-
culates the coefficients of a third order polynominal 
equation. An additional circuit interpolates between two 
data points. As the initial condition circuit receives a 
new data point, it drops the oldest point and computes 
new coefficients for the interpolator. The interpolator 
output is a smooth (piecewise) continuous signal. 
An analog computer simulation of the third order 
digital-to-analog converter showed, that for normalized 
sampling frequencies above five samples per cycle, a con-
verter which uses third order interpolation provides the 
same results as a conventional sample and hold digital-
to-analog converter with twice the normalized sample 
rate. Incorporating a third order interpolator into a
digital-to-analog converter will provide better accuracy 
or will permit lower sampling rates to be used with a 
commensurate saving in system bandwidth. 
Note:
Requests for further information may be directed 
to:
Technology Utilization Officer 
Manned Spacecraft Center, Code JM7 
Houston, Texas 77058 
Reference: TSP72-1 0030 
Patent status: 
This invention is owned by NASA, and a patent 
application has been filed. Royalty-free, nonexclusive 
licenses for its commercial use will be granted by NASA. 
Inquiries concerning license rights should be made to: 
Paten Patent Counsel 
Code AM 
NASA Manned Spacecraft Center 
Houston, Texas 77058
Source: W. P. Dotson

Manned Spacecraft Center

(MSC-1 2458) 
Category: 02 
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Third order digital-to-analog converter

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