GC5016 Datasheet, PDF (44/88 Pages) Texas Instruments – WIDEBAND QUAD DIGITAL DOWN CONVERTER/ UP CONVERTER

GC5016
SLWS142G − JANUARY 2003 − REVISED NOVEMBER 2005
NCO
www.ti.com
AI
AFS
ACK
TINF
GAIN
PFIR
Dual CIC
B
TDM
Broadcast
C
D
SUM
and
FORMAT
IFLG
AO [15:0]
BO [15:0]
CO [15:0]
DO [15:0]
Figure 22. Normal Mode Transmit Channel
14.6.1 splitIQ Mode
The SplitIQ mode uses channels A,B and C,D in pairs. The PFIR and CIC are used with real data into channel A or
C, and imaginary data into channels B or D. Figure 22 shows the standard configuration. The difference is that PFIR,
CIC A/C processes the I channels, and PFIR, CIC B/D processes only the Q channels. Channels B and D are
programmed as if real data is processed. The I and Q combination is done in the Channel A and C Mixer.
The SplitIQ mode can use the TDM IQ , and parallel I Q(16bit 2 ports) input modes. Each CIC is configured for the
I input data. The CIC channel A,C I, and B,D Q are modulated using mixers A and C. For the complex mixer, the XQ
input connects the B and D CIC I outputs.
The A and C Mixers are programmed with the freq differential phase, and phase, phase offset value. There are
pseudo-commands splitiq_AB and splitiq_CD for setting only one pair of channels in splitiq mode. The PFIR in this
configuration has twice the number of taps versus the standard configuration. This mode has the added benefit of
allowing the CIC filter to be bypassed.
14.7 Double Rate Mode
Figure 23 shows the double rate data flows from input to mixer output. The double rate mode input configuration
follows the splitIQ mode for the Transmit Input and PFIR configuration. The real portion of the data must be entered
to channel A, and the imaginary to channel B. TDM input may be used if desired. The filters A and B are configured
to process real data. Each dual CIC is configured to accept real input and interpolate (by an even ratio), and outputs
two samples per clock. The output of CICA is then I(2k) and I(2k+1), while the output of CICB is Q(2k) and Q(2k+1).
Mixer A is configured to accept cross-strapped input for the qcos and qsin multipliers, so that mixer A input is I(2k)
and Q(2k). Similarly, mixer B is configured to accept cross-strapped input for the icos and isin multipliers, so that mixer
B input is I(2k+1) and Q(2k+1). The output sample rate (fsample) is twice the chip clock rate (CK).
The cmd5016 configuration software controls this mode when the pseudo-command tout_rate is set to 2. The
cmd5016 configuration software sets the proper CIC and mixer settings. The user must provide the tuning frequency
(freq). In double-rate mode, the accumulated value in the NCO should be increased by 2 x (ftune / fsample) x 2³²
or (ftune / CK) x 2³². This is set directly in freq_msb, freq_mid, and freq_lsb or by setting freq and fck in the software.
The phase setting for NCO B should be offset from A by one frequency step, so phase(NCO_B) = phase(NCO_A)
+ (ftune / fsample) x 2¹⁶. NCO B gets a phase offset of (ftune / fsample) x 2¹⁶.
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