AD9753ASTZRL Analog Devices Inc, AD9753ASTZRL Datasheet - Page 20

• Manufacturer Part Number: AD9753ASTZRL
• Description: 12-Bit, 300 MSPS TxDAC+ DAC
• Manufacturer: Analog Devices Inc
• Series: TxDAC+®r

Specifications of AD9753ASTZRL

• Settling Time: 11ns
• Number Of Bits: 12
• Data Interface: Parallel
• Number Of Converters: 1
• Voltage Supply Source: Analog and Digital
• Power Dissipation (max): 165mW
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-LQFP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: AD9753-EB - BOARD EVAL FOR AD9753
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

AD9753
Effects of Noise and Distortion on Bit Error Rate (BER)
Textbook analyses of Bit Error Rate (BER) performance are
generally stated in terms of E (energy in watts-per-symbol or
watts-per-bit) and NO (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 quadra-
ture PAM signal (i.e., M = 8 for 64 QAM, M = 16 for 256 QAM).
Figure 32 implies gray coding in the QAM constellation, as well
as the use of matched filters at the receiver, which is typical.
The horizontal 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 neces-
sary. To calculate 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/NO) 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 strongest
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/NO 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 and 7). When
used to synthesize high level QAM signals as described above,
noise, as opposed to distortion, will dominate its performance in
these applications.
COMMENT A: 25 MSYMBOL, 64 QAM CARRIER @ 825MHz
–100
–110
–120
–20
–30
–40
–50
–60
–70
–80
–90
Frequency of 800 MHz
Figure 31. Signal of Figure 28 Mixed to Carrier
CENTER 860MHz
2
1
C11
MARKER 1 [T2]
859.91983968MHz
C11
–99.88dBm
C0
11MHz/
CH PWR
ACP UP
ACP LOW
1
VBW
RBW
SWT
1 [T2]
1 [T2]
2 [T2]
C0
10kHz
10kHz
2.8 s
+859.91983968MHz
–49.91983968MHz
–49.91983968MHz
Cu1
RF ATT
UNIT
–99.88bBm,
SPAN 110MHz
–65.67dBm
–65.15dBm
–7.05dBm
33.10dB
33.10dB
Cu1
0dB
dBm
2MA
–20–
Pseudo Zero Stuffing/IF Mode
The excellent dynamic range of the AD9753 allows its use in
applications where synthesis of multiple carriers is desired. In
addition, the AD9753 can be used in a pseudo zero stuffing
mode that improves dynamic range at IF frequencies. In this
mode, data from the two input channels is interleaved to the
DAC, which is running at twice the speed of either of the input
ports. However, the data at Port 2 is held constant at midscale.
The effect of this is shown in Figure 33. The IF signal is the
image, with respect to the input data rate, of the fundamen-
tal. Normally, the sinx/x response of the DAC will attenuate
this image. Zero stuffing improves the pass-band flatness so that
the image amplitude is closer to that of the fundamental sig-
nal. Zero stuffing can be an especially useful technique in the
synthesis of IF signals.
Figure 32. Probability of a Symbol Error for QAM
Figure 33. Effects of Pseudo Zero Stuffing on
Spectrum of AD9753
1E–0
1E–1
1E–2
1E–3
1E–4
1E–5
1E–6
–10
–20
–30
–40
–50
0
0
0
ZERO STUFFING
FREQUENCY (Normalized to Input Data Rate)
4 QAM
AMPLITUDE
OF IMAGE
WITHOUT
5
0.5
16 QAM
SNR/BIT (dB)
10
1
64 QAM
AMPLITUDE
OF IMAGE
USING
ZERO STUFFING
15
1.5
20
REV. B
2
20