GC5316_14 Datasheet, PDF (39/76 Pages) Texas Instruments – HIGH-DENSITY DIGITAL DOWNCONVERTER AND UPCONVERTER

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GC5316
SLWS154A − JANUARY 2004 − REVISED MARCH 2004
The phase of the NCO’s 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 determine by the following formula:
Phase Offset Word= 2¹⁶ x Offset_in_Degrees / 360 or,
Phase Offset Word= 2¹⁶ x Offset_in_Radians / 2π
Table 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, which 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 zero phase 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. The NCOs used in the transmit
section are identical to what is described for the receive section.
VARIABLE
ssel_nco(2:0)
ssel_dither(2:0)
ssel_freq(2:0)
ssel_phase(2:0)
Table 15. Programming
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
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