Specifications

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SLWS142J − JANUARY 2003 − REVISED AUGUST 2007
www.ti.com
16
2
rea
l
AI
BI
CI
DI
mix_rcv_sel
2
GND XI
TI
mix_icos
20
cos
mix_inv_icos
2
GND XI
TI
mix_isin
20
sin
mix_inv_isin
mix_rcv_cmplx
2
AQ
BQ
CQ
DQ
2
GND XQ
TQ
mix_qcos
20
mix_inv_qcos
2
GND XQ
TQ
mix_qsin
20
mix_inv_qsin
ima
g
2120
16
18
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 × 2
48
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 = (2
16
) 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.