GC5316 Datasheet, PDF (11/75 Pages) Texas Instruments – HIGH-DENSITY DIGITAL DOWNCONVERTER AND UPCONVERTER

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GC5316
SLWS154A − JANUARY 2004 − REVISED MARCH 2004
a) Plot Without Dither or Phase Initialization
b) Plot With Dither and Phase Initialization
Figure 10. NCO Peak Spur Plot
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 rx_distribution or rxclk / (tadj_interp_decim + 1). 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 milli-Hertz (mHz). The frequency word is determined by the following formula:
Frequency Word (in decimal) + 2³²
Tuning Frequency
F _clk
Note that frequency tuning words can be positive or negative valued. Specifying a positive frequency value translates
negative frequencies upwards towards 0 Hz. Specifying a negative tuning frequency translates positive frequencies
downwards towards 0 Hz.
Table 9. Programming
VARIABLE
phase_add_a(31:0)
phase_add_b(31:0)
DESCRIPTION
32-bit tuning frequency word for the A-side DDC when in CDMA mode. Also for UMTS mode.
32-bit tuning frequency word for the B-side DDC when in CDMA mode. Not used in UMTS mode.
Each of the 24 CDMA DDC channels can be loaded with unique frequency words.
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 formula:
Phase Offset Word + 2¹⁶
Offset
in Degrees
360
or
Phase Offset Word + 2¹⁶
Offset in Radians
2p
VARIABLE
phase_offset_a(15:0)
phase_offset_b(15:0
Table 10. Programming
DESCRIPTION
16-bit phase offset word for the A-side DDC when in CDMA mode. Also for UMTS mode.
16-bit phase offset word for the B-side DDC when in CDMA mode. Not used in UMTS mode.
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