AD9753 Datasheet, PDF (19/26 Pages) Analog Devices – 12-Bit, 300 MSPS High-Speed TxDAC+D/A Converter

AD9753
DV_DD AV_DD
CLK+ CLK– PLLLOCK
PLL/DIVIDER
PORT 1
DATA
INPUT
INPUT
LATCHES
I_OUTA
DAC
PORT 2
DATA
INPUT
FSADJ
INPUT
LATCHES
I_OUTB
AD9753
RSET2
1.9k⍀
REFIO ACOM1 ACOM DCOM
0.1␮F
50⍀
50⍀
0.1␮F
0.1␮F
68⍀ 68⍀
INPP
INPM
OUTP
OUTM
LOIM
LOIP
AD8343 ACTIVE MIXER
LOINPUT
0.1␮F
0.1␮F
M/A-COM ETC-1-1-13 WIDEBAND BALUM
Figure 30. QAM Transmitter Architecture Using AD9753 and AD8343 Active Mixer
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1
2
–70
MARKER 1 [T2]
RBW 10kHz RF ATT 0dB
–99.88dBm VBW 10kHz
859.91983968MHz SWT 2.8 s UNIT
dBm
1 [T2]
–99.88bBm,
+859.91983968MHz
CH PWR
–65.67dBm
ACP UP
–65.15dBm
ACP LOW
–7.05dBm
1 [T2]
33.10dB
–49.91983968MHz
2 [T2]
33.10dB
–49.91983968MHz
2MA
–80
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C11
C11
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CENTER 860MHz
1
C0
C0
11MHz/
Cu1
Cu1
SPAN 110MHz
COMMENT A: 25 MSYMBOL, 64 QAM CARRIER @ 825MHz
Figure 31. Signal of Figure 28 Mixed to Carrier
Frequency of 800 MHz
Effects of Noise and Distortion on Bit Error Rate (BER)
Textbook analysis’ of Bit Error Rate (BER) performance are
generally stated in terms of E (energy in watts-per-symbol or
watts-per-bit) and N_O (spectral noise density in watts/Hz). For
QAM signals, this performance is shown graphically in Figure
32. M represents the number of levels in each quadrature PAM
signal (i.e., M = 8 for 64 QAM, M = 16 for 256 QAM). Figure
32 implies grey coding in the QAM constellation, as well as the
use of matched filters at the receiver, which is typical. The hori-
zontal axis of Figure 32 can be converted to units of energy/
symbol by adding to the horizontal axis 10 log of the number of
bits in the desired curve. For instance, to achieve a BER of 1e-6
with 64 QAM, an energy per bit of 20 dB is necessary. To cal-
culate energy per symbol, we add 10 log(6), or 7.8 dB. 64 QAM
with a BER of 1e-6 (assuming no source or channel coding) can
therefore theoretically be achieved with an energy/symbol-to-
noise (E/N_O) ratio of 27.8 dB. Due to the loss and interferers
inherent in the wireless path, this signal-to-noise ratio must be
realized at the receiver to achieve the given bit error rate.
Distortion effects on BER are much more difficult to determine
accurately. Most often in simulation, the energies of the stron-
gest distortion components are root-sum-squared with the noise,
and the result is treated as if it were all noise. That being said, if
the example above of 64 QAM with the BER of 1e-6, using the
E/N_O ratio is much greater than the worst-case SFDR, the noise
will dominate the BER calculation.
The AD9753 has a worst-case in band SFDR of 47 dB at the
upper end of its frequency spectrum (see TPCs 4, 7). When
used to synthesize high-level QAM signals as described above,
noise, as opposed to distortion, will dominate its performance in
these applications.
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4 QAM 16 QAM
64 QAM
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0
5
10
15
20
SNR/BIT – dB
Figure 32. Probability of a Symbol Error for QAM
REV. 0
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