AD9751AST View Datasheet(PDF) - Analog Devices

Part Name

Description

Manufacturer

AD9751AST

10-Bit, 300 MSPS High Speed TxDAC+® D/A Converter

Analog Devices 

AD9751

DVDD AVDD

CLK+ CLK– PLLLOCK

PLL/DIVIDER

PORT 1

DATA

INPUT

INPUT

LATCHES

IOUTA

DAC

PORT 2

DATA

INPUT

FSADJ

INPUT

LATCHES

IOUTB

AD9751

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 BALUN

Figure 30. QAM Transmitter Architecture Using AD9751 and AD8343 Active Mixer

MARKER 1 [T2]

–100.59dBm

859.91983968MHz

–20

–30

–40

–50

–60

1

2

–70

RBW

VBW

SWT

10kHz RF ATT 0dB

10kHz

2.8 s UNIT dBm

1 [T2]

CH PWR

ACP UP

ACP LOW

1 [T2]

2 [T2]

–100.59bBm,

+859.91983968MHz

–64.88dBm

–62.26dBm

–7.38dBm

33.48dB

–49.91983968MHz

33.10dB

–49.91983968MHz

2MA

–80

–90

–100

C11

C11

–110

–120

CENTER 860MHz

1

Cu1

Cu1

C0

C0

11MHz/

SPAN 110MHz

COMMENT A: 25 MSYMBOL, 64 QAM CARRIER @ 825MHz

Figure 31. Signal of Figure 27 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 is

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 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-

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, using

the example above of 64 QAM with the BER of 1e-6, if the E/NO

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.

1E0

1E–1

1E–2

1E–3

4 QAM 16 QAM

64 QAM

1E–4

1E–5

1E–6

0

5

10

15

20

SNR/BIT (dB)

Figure 32. Probability of a Symbol Error for QAM

–20–

REV. C

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