MT8888C
Data Sheet
9.0 Single Tone Generation
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.
OUTPUT FREQUENCY (Hz)
ACTIVE
%ERROR
INPUT
SPECIFIED
ACTUAL
L1
L2
L3
L4
H1
H2
H3
H4
697
770
699.1
766.2
+0.30
-0.49
-0.54
+0.74
+0.57
-0.32
-0.35
+0.73
852
847.4
941
948.0
1209
1336
1477
1633
1215.9
1331.7
1471.9
1645.0
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.
V22f + V23f + V24f + .... V2
nf
THD (%) = 100
Vfundamental
Figure 11 - Equation 1. THD (%) For a Single Tone
The Fourier components of the tone output correspond to V2f.... Vnf as measured on the output waveform. The total
harmonic distortion for a dual tone can be calculated using Equation 2. VL and VH correspond to the low group
amplitude and high group amplitude, respectively and V2IMD 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.
V22L + V23L + .... V2nL + V2
+
2H
V23H + .. V2nH + V2
IMD
THD (%) = 100
V2L + V2
H
Figure 12 - Equation 2. THD (%) For a Dual Tone
11
Zarlink Semiconductor Inc.
ZARLINK [ ZARLINK SEMICONDUCTOR INC ]
