MT8888C
9.0
Single Tone Generation
Data Sheet
A single tone mode is available whereby individual tones from the low group or high group can be generated. This
mode can be used for DTMF test equipment applications, acknowledgment tone generation and distortion
measurements. Refer to Control Register B description for details.
ACTIVE
INPUT
L1
L2
L3
L4
H1
H2
H3
H4
OUTPUT FREQUENCY (Hz)
%ERROR
SPECIFIED
697
770
852
941
1209
1336
1477
1633
ACTUAL
699.1
766.2
847.4
948.0
1215.9
1331.7
1471.9
1645.0
+0.30
-0.49
-0.54
+0.74
+0.57
-0.32
-0.35
+0.73
Table 2 - Actual Frequencies Versus Standard Requirements
10.0
Distortion Calculations
The MT8888C 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 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
22f
+ V
23f
+ V
24f
+ .... V
2nf
THD (%) = 100
V
fundamental
Figure 11 - 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 using Equation 2. V
L
and V
H
correspond to the low group
amplitude and high group amplitude, respectively and V
2IMD
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
Figure 12 - Equation 2. THD (%) For a Dual Tone
11
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
