GC5316 Datasheet, PDF (9/75 Pages) Texas Instruments – HIGH-DENSITY DIGITAL DOWNCONVERTER AND UPCONVERTER

www.ti.com
Table 6. Bus Selection
GC5316
SLWS154A − JANUARY 2004 − REVISED MARCH 2004
SELECT VALUE
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
DATA TAKEN FROM RX_DISTRIBUTION BUS
I Data
Q Data
Bus a
Bus a
Bus b
Bus b
Bus c
Bus c
Bus d
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 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 + 2^mixer_gain*2
VARIABLE
ddcmux_sel_a(3:0)
ddcmux_sel_b(3:0)
remix_only
ch_rate_sel(1:0)
mixer_gain
Table 7. Programming
DESCRIPTION
Programs the I and Q complex input data routing onto two of the four input ports for stream A of CDMA DDC
Programs the I and Q complex input data routing onto two of the four input ports for stream B of CDMA DDC
Set to 0 for complex input data, or to 1 for real data
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.
When asserted adds 6 dB of gain in the mixer. This gain is highly recommended.
9