GC5016 Datasheet, PDF (16/88 Pages) Texas Instruments – WIDEBAND QUAD DIGITAL DOWN CONVERTER/ UP CONVERTER

GC5016
SLWS142G − JANUARY 2003 − REVISED NOVEMBER 2005
BI DI
AI CI
2
mix_rcv_sel
TI mix_rcv_cmplx
GND XI
2
mix_icos
BQ DQ
AQ CQ
16
2
TQ
GND XQ
18
2
mix_qcos
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mix_inv_icos
mix_inv_qcos
20
cos
TI
GND XI
20
real
TQ
GND XQ
2
mix_isin
2
mix_qsin
mix_inv_isin
mix_inv_qsin
20
20
sin
20
21
imag
Figure 5. Multiplexing Options in Mixer
13.6 Numerically Controlled Oscillator (NCO)
The tuning frequency of each up-converter is specified as a 48-bit word and the phase offset is specified as a 16-bit
word. The 48-bit tuning word is calculated based on:
Freq words = FTune(negative for DDC) / CK × 2⁴⁸
The NCO phase is computed as the integrated frequency word phase + phase_offset + dither. A block diagram of
the NCO circuit is shown in Figure 6. The tuning frequency is set to FREQ according to the formula FREQ = (248)
x F/fCK, where F is the desired tuning frequency and fCK is the chip’s clock rate. The 16-bit phase offset setting is
phase = (2¹⁶) x Ph/2π , where Ph is the desired phase in radians ranging between 0 and 2π.
A negative tuning frequency should be used for down-conversion. A positive tuning frequency can be used to flip the
spectrum of the desired signal (if the input is real). FREQ and phase are set as shown in Table 53 through Table 56
or in software by specifying freq_msb, freq_mid, freq_lsb, and phase. The configuration software calculates the
appropriate settings for freq_msb, freq_mid, and freq_lsb given the chip clock frequency (fCK) and freq. (If both freq
and freq_msb are set freq_msb takes priority). The calculation includes the effects of zpad and double rate
processing. Both fck and freq are expressed in Mhz.
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