GC5316 datasheet(11/75 Pages) TI

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GC5316

SLWS154A − JANUARY 2004 − REVISED MARCH 2004

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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 Fclk/ 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

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

DESCRIPTION

phase_add_a(31:0)

32-bit tuning frequency word for the A-side DDC when in CDMA mode. Also for UMTS mode.

phase_add_b(31:0)

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

Phase Offset Word

+ 216

Offset in Radians

Table 10. Programming

VARIABLE

DESCRIPTION

phase_offset_a(15:0)

16-bit phase offset word for the A-side DDC when in CDMA mode. Also for UMTS mode.

phase_offset_b(15:0

16-bit phase offset word for the B-side DDC when in CDMA mode. Not used in UMTS mode.

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