GC5018_06 Datasheet, PDF (19/134 Pages) Texas Instruments – 8-CHANNEL WIDEBAND RECEIVER

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GC5018
8-CHANNEL WIDEBAND RECEIVER
SLWS169A – MAY 2005 – REVISED NOVEMBER 2005
a) Worst Case Spectrum Without Dither
Figure 3-17. NCO SFDR - Without Dither
b) Spectrum With Dither (Tuned to Same Frequency
Figure 3-18. NCO SFDR - With Dither
Frequency − Fs
a) Plot Without Dither or Phase Initialization
Figure 3-19. NCO Spectra (0 and Fs/4) - Without Dither or
Phase Initialization
Frequency − Fs
b) Plot With Dither or Phase Initialization
Figure 3-20. NCO Spectra (0 and Fs/4) - With Dither or
Phase Initialization
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 frequency resolution is Fclk/ 2³². As an example, at an input clock
rate of 61.44 MHz, the frequency step size would be approximately 14 milli-Hertz. The Frequency Word is
determined by the formula:
Frequency Word (in decimal)= 2³² x Tuning Frequency / F_clk
Note that frequency tuning words can be positive or negative valued. Specifying a positive frequency
value translates complex negative frequencies upwards towards 0 Hertz. Specifying a negative tuning
frequency translates complex positive frequencies downwards towards 0 Hertz.
VARIABLE
phase_add_a(31:0)
phase_add_b(31:0)
FREQUENCY PROGRAMMING
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 16 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 m°. The Phase Offset Word is determined by the formula:
Phase Offset Word = 2¹⁶ x Offset_in_Degrees / 360 or,
Phase Offset Word = 2¹⁶ x Offset_in_Radians / 2π
RECEIVE DIGITAL SIGNAL PROCESSING
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