AD9782 Datasheet, PDF (29/52 Pages) Analog Devices – 12-Bit, 200 MSPS/500 MSPS TxDAC+ with 2 x /4 x /8 x Interpolation and Signal Processing

Preliminary Technical Data
MODULATION MODES
Table 29. Single Channel Modulation
MODDUAL
CHANNEL
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
1
MOD[1]
0
0
1
1
0
0
1
1
Either channel of the AD9782’s interpolation filter channels can
be routed to the DAC and modulated. In single channel
operation the input data may be modulated by a real sinusoid;
the input data and the modulating sinusoid will contain both
positive and negative frequency components. A double
sideband output results when modulating two real signals. At
the DAC output the positive and negative frequency
components will add in phase resulting in constructive signal
summation.
As the modulating sinusoidal frequency becomes a larger
fraction of the DAC update rate, fDAC, the more the sinc function
of the DAC shapes the modulated signal bandwidth, and the
closer the first image moves. As the AD9782 interpolation
filter’s pass band represents a large portion of the input data’s
Nyquist band, under certain modulation and interpolation
modes it is possible for modulated signal bands to touch or
overlap images if sufficient interpolation is not used.
Figure 48 shows the effect of real modulation under all
interpolation modes. The sinc shaping at the corners of the
modulated signal band and the bandwidth to the first image for
those cases whose pass bands do not touch or overlap are
tabulated.
AD9782
MOD[0]
0
1
0
1
0
1
0
1
Mode
I Channel, no modulation
I Channel, modulation by fDAC/2
I Channel, modulation by fDAC/4
I Channel, modulation by fDAC/8
Q Channel, no modulation
Q Channel, modulation by fDAC/2
Q Channel, modulation by fDAC/4
Q Channel, modulation by fDAC/8
Table 30.
Modulation
none
fDAC/2
fDAC/4
fDAC/8
None
fSIN
fSIN
Overlap
Overlap
Interpolation
×2
×4
2 fSIN
4 fSIN
2 fSIN
4 fSIN
Touching 2 fSIN
Overlap Touching
×8
8 fSIN
8 fSIN
4 fSIN
6 fSIN
Table 31.
Modulation
None
fDAC/2
fDAC/4
fDAC/8
None
0
–2.8241
–0.0701
–22.5378
Overlap
Overlap
Interpolation
×2
×4
0
0
–0.6708 –0.1657
–1.1932 –2.3248
–9.1824 –6.1190
Touching –0.2921
–1.9096
Overlap Touching
Modulated pass band edges sinc shaping(lower/upper).
×8
0
–0.0413
–3.0590
–4.9337
–0.5974
–1.3607
–0.0727
–0.4614
Rev. PrC | Page 29 of 52