CMX980AL7 Ver la hoja de datos (PDF) - MX-COM Inc

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CMX980AL7

Digital Radio Baseband Processor

MX-COM Inc  

Digital Radio Baseband Processor

7

3 External Components

3.1 Rx Inputs

When using the internal anti-alias filter, the following is recommended:

CMX980A Advance Information

Figure 2: Recommended External Components - Rx Input

Example Values: MCLK = 9.216MHz

R1 = 220Ω

R2 = 1.2kΩ

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%)

Table 2: Recommended External Components - Rx Inputs

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 4.4.1. In both cases, there should be at least one filter pole close to the chip inputs.

3.2 Tx Outputs

Figure 3: Recommended External Components - Tx Outputs

Example Values: MCLK = 9.216MHz

R3 = 6.2kΩ

C3 = 1nF (R3 x C3 product, giving –3dB at 25kHz, should be preserved within 10%)

Table 3: Recommended External Components - Tx Outputs

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 4.4.1.

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 5.4 for further details.

2000 MX-COM, Inc.

www.mxcom.com tel: 800 638 5577 336 744 5050 fax: 336 744 5054

Doc. 20480201.001

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