GC5316 datasheet(9/75 Pages) TI

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GC5316

SLWS154A − JANUARY 2004 − REVISED MARCH 2004

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Table 6. Bus Selection

SELECT VALUE

DATA TAKEN FROM RX_DISTRIBUTION BUS

I Data

Q Data

Bus a

Bus b

Bus c

Bus d

Bus a

Bus b

Bus a

Bus c

Bus a

Bus d

Bus b

Bus a

Bus b

Bus c

Bus b

Bus d

Bus c

Bus a

Bus c

Bus b

Bus c

Bus d

Bus a

Bus d

Bus b

Bus d

Bus c

The receive mixer translates the input from selector to baseband where subsequent filtering is performed to isolate

the signal of interest. The mixer is a complex multiplier that accepts 18-bit I and 18-bit Q signal data from the receive

input interface and 20-bit sine and cosine sequences from the NCO. The NCO generates a mixing frequency

(sometimes referred to as a local oscillator, or LO) specified by the user so that the desired signal of interest is tuned

to 0 Hz. The NCO is discussed in detail in the next section.

A DDC channel can support one UMTS signal directly, or two CDMA channels at half the input rate. When in CDMA

mode each channel may set the path selection, the mixer tuning and phase independently. The mixer output produces

two complex streams; one representing the signal path for the A-side DDC, the other the B-side. Each of these

streams drives a channel delay and zero pad block.

The maximum input rate for UMTS is rxclk for either real or complex input data. The maximum rx_distribution rate

in CDMA mode (real or complex inputs) is rxclk/2. When adcclk/rxclk >

1/2, this is normally accomplished using the

resampler. For unusual cases where adcclk/rxclk = 1 and the resampler is not used, cdma_mode must be zero so

only one signal can be processed in a DDC block, even if it is a CDMA signal.

The mixer gain is:

Gain

+ 2mixer_gain*2

Table 7. Programming

VARIABLE

DESCRIPTION

ddcmux_sel_a(3:0)

Programs the I and Q complex input data routing onto two of the four input ports for stream A of CDMA DDC

ddcmux_sel_b(3:0)

Programs the I and Q complex input data routing onto two of the four input ports for stream B of CDMA DDC

remix_only

Set to 0 for complex input data, or to 1 for real data

ch_rate_sel(1:0)

Informs the DDC of the rx_distribution bus rate (1, 1/2, 1/4, or 1/8 rxclk for settings 0, 1, 2, or 3 respectively.

Note this parameter must be the same in all enabled DDC blocks.

mixer_gain

When asserted adds 6 dB of gain in the mixer. This gain is highly recommended.

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