CMX980AL7 CML Microcircuits, CMX980AL7 Datasheet - Page 98

• Manufacturer Part Number: CMX980AL7
• Description: TETRA Baseband Processor
• Manufacturer: CML Microcircuits

TETRA Baseband Processor
Rx Notes:
General Points:
1999 Consumer Microcircuits Limited
1. Note this means 0.85V or 0.56V on each input of the differential pair.
2. Both measured with MCLK/4096 Hz test signal, in MCLK/1024 Hz bandwidth.
3. Extrapolated from third harmonic distortion at maximum signal.
4. Output via the serial interface at MCLK/2 or MCLK/4.
5. These anti-alias filter requirements can be supplied by IF channel filtering, baseband filtering
6. With respect to maximum input level.
7. This should be supplied by a network equivalent to Figure 2.
8. These figures assume that 10-15dB attenuation at MCLK/4 is provided by IF channel filtering
9. With default coefficients and internal anti-alias filter selected
10. Offset adjustment for each channel is available by loading a 16-bit word into the receive offset
11. Optimally, as much anti-alias filtering as possible should be carried out prior to any AGC
12. Anti-alias filter requirements quoted are for mobile station applications. For base station
or a combination of both. It is recommended that, in order to maximise the performance
obtained from the CMX980A for TETRA applications, at least 10dB and 25dB attenuation be
provided at MCLK/70 and MCLK/4 respectively, prior to an external AGC function. Other
applications may require less stringent external filtering.
or by additional filtering at baseband. Note that the recommended configuration shown in
Figure 2a includes an AGC after the 32kHz pole
register via the serial interface.
function before the receive inputs. This allows the AGC to act on a reduced bandwidth signal
and thereby improve the relative magnitude of the wanted part. The device has been designed
to reduce the complexity of any external anti-alias filter as much as possible and a 4-pole
Butterworth or 3-pole Chebyshev with a -3dB point at about MCLK/150 should be adequate.
The internal anti-alias filter, if used, cannot provide the required 110dB attenuation at MCLK/4
and must be supplemented by external filtering. An example of a suitable external filter
structure is shown in Figure 2a.
applications, all attenuation figures should be increased by 3dB.
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CMX980A
D/980A/3