AD9751 Analog Devices, AD9751 Datasheet - Page 20

• Manufacturer Part Number: AD9751
• Manufacturer: Analog Devices

Specifications of AD9751

• Resolution (bits): 10bit
• Dac Update Rate: 300MSPS
• Dac Settling Time: 11ns
• Max Pos Supply (v): +3.6V
• Single-supply: Yes
• Dac Type: Current Out
• Dac Input Format: Par

AD9751
Effects of Noise and Distortion on Bit Error Rate (BER)
Textbook analysis of Bit Error Rate (BER) performance is
generally stated in terms of E (energy in watts-per-symbol or
watts-per-bit) and N
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 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 necessary. To
calculate energy per symbol, add 10 log(6) or 7.8 dB. Therefore
64 QAM with a BER of 1e-6 (assuming no source or channel
coding) can theoretically be achieved with an energy/symbol-
Figure 31. Signal of Figure 27 Mixed to Carrier
Frequency of 800 MHz
COMMENT A: 25 MSYMBOL, 64 QAM CARRIER @ 825MHz
–100
–110
–120
–20
–30
–40
–50
–60
–70
–80
–90
CENTER 860MHz
2
C11
1
MARKER 1 [T2]
–100.59dBm
859.91983968MHz
RSET2
1.9k
PORT 1
PORT 2
INPUT
INPUT
FSADJ
DATA
DATA
C11
O
Figure 30. QAM Transmitter Architecture Using AD9751 and AD8343 Active Mixer
(spectral noise density in watts/Hz). For
0.1 F
CLK+ CLK– PLLLOCK
C0
REFIO ACOM1 ACOM DCOM
11MHz/
LATCHES
LATCHES
INPUT
INPUT
CH PWR
ACP UP
ACP LOW
1
RBW
VBW
SWT
1 [T2]
1 [T2]
2 [T2]
C0
10kHz RF ATT
10kHz
2.8 s
AD9751
+859.91983968MHz
–49.91983968MHz
–49.91983968MHz
Cu1
PLL/DIVIDER
DVDD AVDD
UNIT
–100.59bBm,
DAC
SPAN 110MHz
–64.88dBm
–62.26dBm
–7.38dBm
33.48dB
33.10dB
I
I
OUTA
OUTB
Cu1
0dB
dBm
50
50
2MA
–20–
0.1 F
0.1 F
68
to-noise (E/N
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, using
the example above of 64 QAM with the BER of 1e-6, if the E/N
ratio is much greater than the worst-case SFDR, the noise will
dominate the BER calculation.
The AD9751 has a worst-case in-band SFDR of 47 dB at the
upper end of its frequency spectrum (see TPCs 2 and 3). When
used to synthesize high level QAM signals as described above,
noise, as opposed to distortion, will dominate its performance
in these applications.
Figure 32. Probability of a Symbol Error for QAM
68
LOINPUT
1E–1
1E–2
1E–3
1E–4
1E–5
1E–6
1E0
0
INPP
INPM
O
) ratio of 27.8 dB. Due to the loss and interferers
AD8343 ACTIVE MIXER
4 QAM
M/A-COM ETC-1-1-13 WIDEBAND BALUN
5
16 QAM
0.1 F
0.1 F
SNR/BIT (dB)
LOIM
LOIP
10
64 QAM
OUTP
OUTM
15
20
REV. C
O