GC4016 datasheet(69/83 Pages) TI

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August 27, 2001

GC4016 MULTI-STANDARD QUAD DDC CHIP

DATA SHEET REV 1.0

This document contains information which may be changed at any time without notice

7.10

EXAMPLE IS-136 DAMPS APPLICATION

This section describes how to configure the chip to downconvert DAMPS signals, apply the root-raised-cosine receive filter,

and output samples at two times, four times or eight times the DAMPS symbol rate. The desired DAMPS Specifications are:

7.10.1 DAMPS Filter Response

Figure 21 shows the overall response using CFIR filter, cfir_68, and a set of RRC PFIR coefficients tuned for 2X oversampled

output data. The DAMPS out of band rejection mask is also shown.

The RRC PFIR coefficients are:

-12 -117 -113 8 127 112 -38 -175 -134 82 275 224 -71 -348 -307 61 398 286 -286 -761

-442 766 1954 1708 -660 -4042 -5641 -2533 6187 18177 28625 32767

These coefficients are available by e-mail or over the web as pfir_damps_2x.taps. The PFIR_SUM for this set of coefficients

is 119387.

7.10.2 Oversampling Using the Resampler

This example assumes the input sample rate is equal to 8*N*B, where N is the decimation in the CIC filter (See Section 5.6)

and B is the DAMPS symbol rate (24.3 KHz). The outputs are two complex samples per symbol (48.6 KHz) with the resampler

set to interpolate by unity (no interpolation). The output rate can be doubled or quadrupled as desired by changing the resampler

Table 31: Desired DAMPS Specifications

Specification

Value

Comment

Clock (CK)

62.208MHz =8*320*24.3KHz

Can be any value equal to 8NB, where N is the CIC decimation ratio and B is the DAMPS

symbol rate of 24.3KHz

Input Sample Rate

Same as clock rate

Can be 1/2, 1/3, 1/4, ... 1/N of the clock rate by using the zero pad feature.

Input Format

A port, 14 Bit, 2’s Complement

Can be modified as desired

Spur free dynamic

range

> -110dB

The GC4016 NCO provides more than 115 dB of spur free dynamic range

Output Sample Rate

48.6KHz, complex data (2X)

Can be 4X, 8X or any multiple of the symbol rate by changing the resampler ratios

Passband Response

RRC with alpha=0.35

Matches the required receive filter

Stopband Rejection

Set by DAMPS Specification

See the DAMPS rejection mask in Figure 21

Output Format

Four serial streams, 24 bit I and Q data

Can be modified as desired

Figure 21. Frequency Response for the Example DAMPS Application

Rejection Mask

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