MT8885
Active
Input
L1
L2
L3
L4
H1
H2
H3
Output Frequency (Hz)
%Error
Specified
697
770
852
941
1209
1336
1477
Actual
699.1
766.2
847.4
948.0
1215.9
1331.7
1471.9
+0.30
-0.49
-0.54
+0.74
+0.57
-0.32
-0.35
Data Sheet
H4
1633
1645.0
+0.73
Table 2 - Actual Frequencies Versus Standard Requirements
6.0
Distortion Calculations
The MT8885 is capable of producing precise tone bursts with minimal error in frequency (see Table 2). The internal
summing amplifier is followed by a first-order lowpass switched capacitor filter to minimize harmonic components
and intermodulation products. The total harmonic distortion for a
single tone
can be calculated by using Equation 1,
which is the ratio of the total power of all the extraneous frequencies to the power of the fundamental frequency
expressed as a percentage.
V
2
2f
+ V
2
3f
+ V
2
4f
+ .... V
2
nf
THD (%) = 100
V
2
fundamental
Equation 1. THD (%) For a Single Tone
The Fourier components of the tone output correspond to V
2f
.... V
nf
as measured on the output waveform. The total
harmonic distortion for a
dual tone
can be calculated by using Equation 2. V
L
and V
H
correspond to the low group
amplitude and high group amplitude, respectively and V
2
IMD
is the sum of all the intermodulation components. The
internal switched-capacitor filter following the D/A converter keeps distortion products down to a very low level as
shown in Figure 10.
V
22L
+
V
23L
+ ....
V
2nL
+
V
22H
+
V
23H
+ ..
V
2nH
+
V
2IMD
THD (%) = 100
V
2L
+
V
2H
Equation 2. THD (%) For a Dual Tone
11
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
