MT8888C Datasheet, PDF (11/25 Pages) Mitel Networks Corporation – Integrated DTMFTransceiver with Intel Micro Interface

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.
ACTIVE
INPUT
OUTPUT FREQUENCY (Hz)
SPECIFIED
ACTUAL
%ERROR
L1
697
699.1
+0.30
L2
770
766.2
-0.49
L3
852
847.4
-0.54
L4
941
948.0
+0.74
H1
1209
1215.9
+0.57
H2
1336
1331.7
-0.32
H3
1477
1471.9
-0.35
H4
1633
1645.0
+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.
THD (%) = 100
V^22L + V^23L + .... V^2nL + V^22H +
V^23H + .. V^2nH + V^2IMD
V^2L + V^2H
Figure 12 - Equation 2. THD (%) For a Dual Tone
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Zarlink Semiconductor Inc.