GC5318 Datasheet, PDF (19/45 Pages) Texas Instruments – HIGH-DENSITY DIGITAL UPCONVERTER

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GC5318
HIGH-DENSITY DIGITAL UPCONVERTER
SLWS187 – JULY 2006
The tuning frequency is specified as a 32-bit frequency word and is programmed as two sequential 16-bit
words over the control port. The NCO operates at the same speed as the txclk/(tadj_interp_decim + 1).
The frequency resolution is simply the F_CLK/ 2³². The NCO frequency resolution is simply the F_CLK/ 2³². As
an example, at an input clock rate of 61.44 MHz, the frequency step size would be approximately 14 MHz.
The frequency word is determined by the formula:
Frequency word (in decimal) = 2³² x Tuning Frequency/F_CLK
NOTE
Frequency tuning words can be positive or negative valued. Specifying a positive
frequency value translates baseband frequencies upward. Specifying a negative tuning
frequency translates baseband frequencies downwards.
Table 2-13. Programming
VARIABLE
phase_add_a(31:0)
phase_add_b(31:0)
DESCRIPTION
32-bit tuning frequency word for the A signal when in CDMA mode. Also for UMTS mode.
32-bit tuning frequency word for the B signal when in CDMA mode. Not used in UMTS mode.
The phase of the NCO Sin/Cos output can be adjusted relative to the phase of other channel NCOs by
specifying a phase offset. The phase offset is programmed as a 16-bit word, yielding a step size of about
5.5 milliDegrees. The phase offset word is determined by the following formula:
Phase Offset Word = 2¹⁶ x Offset_in_Degrees / 360; or,
Phase Offset Word = 2¹⁶ x Offset_in_Radians / 2π
Table 2-14. Programming
VARIABLE
phase_offset_a(15:0)
phase_offset_b(15:0)
DESCRIPTION
16-bit phase offset word for the A signal when in CDMA mode. Also for UMTS mode.
16-bit phase offset word for the B signal when in CDMA mode. Not used in UMTS mode.
Various synchronization signals are available that are used to synchronize the NCOs of all channels with
respect to each other. Frequency sync and phase offset sync determine when frequency and phase offset
changes occur. For example, generating a frequency sync after programming the two frequency words
causes the NCO (or multiple NCOs) to change frequency at that time, rather than after each of the three
frequency words is programmed over the control bus. The NCO accumulator reset sync signal is used to
force the sine and cosine oscillators to their zero phase state. Dither sync can be used to synchronize the
dither generators of multiple NCOs.
Table 2-15. Programming
VARIABLE
ssel_nco(2:0)
ssel_dither(2:0)
ssel_freq(2:0)
ssel_phase(2:0)
DESCRIPTION
Sync source for NCO accumulator reset
Sync source for NCO dither reset
Sync source for NCO frequency register loading
Sync source for NCO phase register loading
GC5318 Operation
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