GC4016 datasheet(9/83 Pages) TI

9 / 83 page

- 4 -

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

3.2

INPUT FORMAT

The chip accept five input formats:

(1) Four input ports of 14 bit data,

(2) Three input ports of 16 bit data,

(3) Two input ports of 14 bit low voltage differential

data, (Contact Graychip for more information)

(4) Three ports of 12 bit with 3 bit exponent floating

point data, and

(5) Three ports of multiplexed, dual channel, 12 bit

with 3 bit exponent floating point data

The 12, 14 and 16 bit input words are in a two’s

complement format. The MSB_POL control bit in address 27

of the channel control pages can be used to convert offset

binary data to the desired two’s complement format. The 3 bit

exponent in the floating point format is an unsigned integer

ranging from 0 to 7. All inputs are converted to the internal 19

bit format at the input to each channel. The 14 and 16 bit

input words are put into the upper 14 and 16 bits respectfully

of the 19 bit word. The unused LSBs are cleared.

The 12 bit floating point word is shifted down and sign

extended by the amount specified by the 3 bit exponent and

then put into the MSBs of 19 bit word.

A crossbar switch allows the user to route any input

source to any downconverter channel.

Table 1 shows the suggested control register settings

required for each input mode. See Section 5.6 for detailed

descriptions of each control setting

Table 1: Input Mode Controls

Control

Address in

Channel Control

Pages 7, 15, 23

and 31

14 bit mode

16 bit mode

14 bit

differential

mode

12 + 3 bit

exponent

mode

Multiplexed

12 + 3 bit

exponent

mode

SHIFT

4 to 7

unused

USE_SHIFT

MIX20B1

INPUT_SEL

0,1,2,3

0,1,2

4,5

0,1,2

SEL_AB

0 or 1

INPUT_MODE

DIFF_IN

4 (Global Page)

NOTES: 1. SHIFT is normally left at 4, see Section 3.3.3 for details.

2. For decimations over 3104, MIX20B should be 0 to allow SHIFT to be less than 4, see Section 3.3.3.

3. INPUT_SEL is used to select the input port used by each channel, 0=port A, 1=portB, 2=port C, 3=portD.

3.3

THE DOWN CONVERTERS

Each down converter contains an NCO and a mixer to

quadrature down convert the signal to baseband, followed by

a 5 stage Cascade Integrate Comb (CIC)1 filter and two

stages of decimate by two filtering to isolate the desired

signal. The signal is then sent to a resampler which can

increase or decrease the final output sample rate to match

the post-processing requirements for baud rate sampling or

oversampling.

A block diagram of the channel is shown in Figure 4.

The INPUT FORMAT circuit converts the selected input

data into the 19 bit format described in Section 3.2. The

ZERO PAD function allows the user to clock the chip at a

higher rate than the input sample rate.

The NCO/Mixer circuit tunes the desired center

frequency down to DC where it is low pass filtered by the

CIC, CFIR, PFIR and Resampler filters.

The

CIC

filter

reduces

the

sample

rate

programmable factor ranging from 8 to 4,096. The CIC

outputs are followed by a coarse gain stage and then

followed by two stages of decimate by 2 filtering. The coarse

gain circuit allows the user to boost the gain of weak signals

up to 42 dB in 6 dB steps. The first stage of the two stage filter

is a 21 tap decimate by 2 filter (CFIR) with user

programmable tap weights. The 21 tap symmetrical lowpass

filter is downloaded into the chip as 12 words, 16 bits each.

This filter is typically programmed to decimate by two, while

1. Hogenhauer, An Economical Class of Digital Filters for Decimation and

Interpolation, IEEE transactions on ASSP, April 1981.

GC4016 датащи(PDF) 9 Page - Texas Instruments

GC4016 датащи(HTML) 9 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83

датащи скачать

ссылки URL