CMX980AL7 CML Microcircuits, CMX980AL7 Datasheet - Page 8

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

TETRA Baseband Processor
1.4
Rx Inputs
When using the internal anti-alias filter, the following is recommended:
Example values (MCLK=9.216MHz):
R1 = 220
R2 = 1.2k
The RC stage formed by R2 and C2 combined with the internal anti-alias filter and Rx FIRs gives a good
approximation to the desired filter characteristics and near-constant group delay over the passband. When not
using the internal anti-alias filter, it is suggested that the user should follow the guidelines in Section 1.5.4.1.
In both cases, there should be at least one filter pole close to the chip inputs.
Tx Outputs
Example values (MCLK=9.216MHz):
R3 = 6.2k
The RC stage formed by R3 and C3 combined with the internal reconstruction filter and the Tx FIRs gives a
good approximation to the desired filter characteristics and near-constant group delay over the passband.
Decoupling capacitors should be employed as detailed in Section 1.5.4.1
When the default master clock frequency is not used, the R2 x C2 and R3 x C3 products may be scaled with
MCLK, but care should be taken to ensure that FIR filter coefficients are designed to compensate for any
amplitude and phase distortion due to both on and off-chip filter components. This compensation is included in
the default filter coefficients. See Section 1.6.4 for further details.
1999 Consumer Microcircuits Limited
External Components
C1 = 1.5nF (R1, C1 precise values are not critical; -3dB at 240kHz)
C2 = 3.9nF (R2 x C2 product, giving -3dB at 32kHz, should be preserved within 10%)
C3 = 1nF (R3 x C3 product, giving -3dB at 25kHz, should be preserved within 10%)
Figure 2b Recommended External Components - Tx Outputs
Figure 2a Recommended External Components - Rx Inputs
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CMX980A
D/980A/3