CMX981 Consumer Microcircuits Limited, CMX981 Datasheet - Page 56

• Manufacturer Part Number: CMX981
• Description: Advanceddigital Radio Baseband Processor (tetra Etc.)
• Manufacturer: Consumer Microcircuits Limited

Advanced Digital Radio Baseband Processor
Rx Notes:
General Points:
 2002 CML Microsystems Plc
1. Note this means 0.85V or 0.56V on each input of the differential pair.
2. Both measured with MCLK/4096 test signal, in MCLK/1024 bandwidth.
3. Extrapolated from third harmonic distortion at maximum signal.
4. These anti-alias filter requirements can be supplied by IF channel filtering, baseband
5. With respect to maximum input level.
6. This should be supplied by a network equivalent to Figure 2a.
7. These figures assume that 10-15dB attenuation at MCLK/4 is provided by IF channel
8. With default coefficients and internal anti-alias filter selected.
9. Offset adjustment for each channel is available by loading a 16-bit word into the receive
10. Optimally, as much anti-alias filtering as possible should be carried out prior to any AGC
11. Anti-alias filter requirements quoted are for mobile station applications. For base station
filtering or a combination of both. It is recommended that in order to maximise the
performance obtained from the CMX981 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.
filtering or by additional filtering at baseband. Note that the recommended configuration
shown in Figure 2a includes an AGC after the 32kHz pole.
offset 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.
56
CMX981
D/981/1