ICM7216A Intersil Corporation, ICM7216A Datasheet - Page 12

• Manufacturer Part Number: ICM7216A
• Description: 8-digit, Multi-function, Frequency Counters/timers
• Manufacturer: Intersil Corporation

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 coefficient of 20
measurement error of 20
FIGURE 14. MAXIMUM ACCURACY OF FREQUENCY AND
FIGURE 16. MAXIMUM ACCURACY FOR FREQUENCY RATIO MEASUREMENT DUE TO LIMITATION OF QUANTIZATION ERRORS
0
2
4
6
8
1
10
10
0.01s
10 CYCLES
0.1s
PERIOD MEASUREMENTS DUE TO LIMITATIONS
OF QUANTIZATION ERRORS
2
3
10s
1 CYCLE
1s
CYCLES
CYCLES
10
PPM
FREQUENCY (Hz)
/
o
C.
10
FREQUENCY MEASURE
3
PERIOD MEASURE
f
OSC
ICM7216A, ICM7216B, ICM7216D
PPM
= 10MHz
0
1
2
3
4
5
6
7
8
1
/
10
o
C will cause a
5
10
10
2
10
7
10
9-21
3
f
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.
A
FIGURE 15. MAXIMUM ACCURACY OF TIME INTERVAL MEA-
10
/f
4
B
10
0
1
2
3
4
5
6
7
8
5
1 CYCLE
10 CYCLES
10
10
1
2
3
CYCLES
CYCLES
SUREMENT DUE TO LIMITATIONS OF QUANTIZA-
TION ERRORS
10
RANGE
MAXIMUM TIME INTERVAL
6
10
10
FOR 10 INTERVALS
7
10
2
10
TIME INTERVAL ( s)
10
8
MAXIMUM TIME INTERVAL
FOR 10
3
10
3
INTERVALS
4
10
5
MAXIMUM TIME
INTERVAL FOR
10
10
2
6
INTERVALS
10
7
10
8