ICM7216A Datasheet, PDF (12/17 Pages) Intersil Corporation – 8-Digit, Multi-Function, Frequency Counters/Timers

ICM7216A, ICM7216B, ICM7216D
Accuracy
In a Universal Counter crystal drift and quantization effects
cause errors. In frequency, period and time interval
modes, a signal derived from the oscillator is used in either
the Reference Counter or Main Counter. Therefore, in
these modes an error in the oscillator frequency will cause
an identical error in the measurement. For instance, an
oscillator temperature
measurement error of
coefficient of
20_PPM /^oC.
20_PPM /^oC
will
cause
a
In addition, there is a quantization error inherent in any digital
measurement of ±1 count. Clearly this error is reduced by dis-
playing more digits. In the frequency mode the maximum
accuracy is obtained with high frequency inputs and in period
mode maximum accuracy is obtained with low frequency
inputs (as can be seen in Figure 14). In time interval mea-
surements there can be an error of 1 count per interval. As a
result there is the same inherent accuracy in all ranges as
shown in Figure 15. In frequency ratio measurement can be
more accurately obtained by averaging over more cycles of
INPUT B as shown in Figure 16.
0
FREQUENCY MEASURE
0.01s
2 0.1s
1s
10s
4
1 CYCLE
10 CYCLES
10² CYCLES
6 ^{103 CYCLES}
PERIOD MEASURE
8
f_OSC = 10MHz
1
10
10³
10⁵
10⁷
FREQUENCY (Hz)
FIGURE 14. MAXIMUM ACCURACY OF FREQUENCY AND
PERIOD MEASUREMENTS DUE TO LIMITATIONS
OF QUANTIZATION ERRORS
0
1
2
3
MAXIMUM TIME INTERVAL
FOR 10³ INTERVALS
4
MAXIMUM TIME
5
INTERVAL FOR
10² INTERVALS
6
MAXIMUM TIME INTERVAL
7
FOR 10 INTERVALS
8
1
10 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷ 10⁸
TIME INTERVAL (µs)
FIGURE 15. MAXIMUM ACCURACY OF TIME INTERVAL MEA-
SUREMENT DUE TO LIMITATIONS OF QUANTIZA-
TION ERRORS
0
1
RANGE
2
3
1 CYCLE
10 CYCLES
4
10² CYCLES
10³ CYCLES
5
6
7
8
1
10 10² 10³ 10⁴ 10⁵ 10⁶ 10⁷ 10⁸
f_A / f_B
FIGURE 16. MAXIMUM ACCURACY FOR FREQUENCY RATIO MEASUREMENT DUE TO LIMITATION OF QUANTIZATION ERRORS
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