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AD9767ASTZRL 参数 Datasheet PDF下载

AD9767ASTZRL图片预览
型号: AD9767ASTZRL
PDF下载: 下载PDF文件 查看货源
内容描述: 10位/ 12位/ 14位, 125 MSPS双通道TxDAC数字 - 模拟转换器 [10-/12-/14-Bit, 125 MSPS Dual TxDAC Digital-to-Analog Converters]
分类和应用: 转换器数模转换器
文件页数/大小: 44 页 / 643 K
品牌: ADI [ ADI ]
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AD9763/AD9765/AD9767  
Data Sheet  
between the two baseband channels. A quadrature mixer  
QUADRATURE AMPLITUDE MODULATION (QAM)  
EXAMPLE USING THE AD9763  
modulates the I and Q components with the in-phase and  
quadrature carrier frequency and then sums the two outputs  
to provide the QAM signal.  
QAM is one of the most widely used digital modulation  
schemes in digital communications systems. This modulation  
technique can be found in FDM as well as spread spectrum  
(that is, CDMA) based systems. A QAM signal is a carrier  
frequency that is modulated in both amplitude (that is, AM  
modulation) and phase (that is, PM modulation). It can be  
generated by independently modulating two carriers of  
identical frequency but with a 90° phase difference. This results  
in an in-phase (I) carrier component and a quadrature (Q) carrier  
component at a 90° phase shift with respect to the I component.  
The I and Q components are then summed to provide a QAM  
signal at the specified carrier frequency.  
10  
DAC  
DSP  
0°  
90°  
CARRIER  
FREQUENCY  
TO  
MIXER  
OR  
Σ
ASIC  
10  
DAC  
NYQUIST  
FILTERS  
QUADRATURE  
MODULATOR  
Figure 83. Typical Analog QAM Architecture  
In this implementation, it is much more difficult to maintain  
proper gain and phase matching between the I and Q channels.  
The circuit implementation shown in Figure 84 helps improve the  
matching between the I and Q channels, and it shows a path for  
upconversion using the AD8346 quadrature modulator. The  
AD9763 provides both I and Q DACs a common reference that  
improves the gain matching and stability. RCAL can be used to  
compensate for any mismatch in gain between the two channels.  
The mismatch can be attributed to the mismatch between RSET1  
and RSET2, the effective load resistance of each channel, and/or  
the voltage offset of the control amplifier in each DAC. The  
differential voltage outputs of both DACs in the AD9763 are  
fed into the respective differential inputs of the AD8346 via  
matching networks.  
A common and traditional implementation of a QAM modulator  
is shown in Figure 83. The modulation is performed in the  
analog domain in which two DACs are used to generate the  
baseband I and Q components. Each component is then typically  
applied to a Nyquist filter before being applied to a quadrature  
mixer. The matching Nyquist filters shape and limit each  
component’s spectral envelope while minimizing intersymbol  
interference. The DAC is typically updated at the QAM symbol  
rate, or at a multiple of the QAM symbol rate if an interpolating  
filter precedes the DAC. The use of an interpolating filter typically  
eases the implementation and complexity of the analog filter, which  
can be a significant contributor to mismatches in gain and phase  
AVDD  
ROHDE & SCHWARZ  
FSEA30B  
OR EQUIVALENT  
0.1µF  
DCOM1/ DVDD1/  
DCOM2 DVDD2  
ACOM AVDD  
RA  
RB  
RA  
SPECTRUM ANALYZER  
RL  
LA  
RL  
VPBF  
I
I
A
B
BBIP  
BBIN  
OUT  
TEKTRONIX  
AWG2021  
WITH  
I DAC  
LATCH  
I
VOUT  
CA  
CB  
DAC  
RB  
OPTION 4  
+
OUT  
LA  
LA  
RL  
RL  
RL  
RL  
CB  
AD9763/  
AD9765/  
AD9767  
WRT1/IQWRT  
LOIP  
LOIN  
CLK1/IQCLK  
RA  
RA  
PHASE  
SPLITTER  
BBQP  
BBQN  
I
I
A
B
RB  
OUT  
Q DAC  
LATCH  
Q
DAC  
CA  
C
FILTER  
RB  
RL  
OUT  
LA  
RL  
WRT2/IQSEL  
AD8346  
VDIFF = 1.82V p-p  
SLEEP  
MODE FSADJ1  
FSADJ2 REFIO  
0.1µF  
DIFFERENTIAL  
RLC FILTER  
ROHDE & SCHWARZ  
SIGNAL GENERATOR  
RL = 200  
RA = 2500Ω  
RB = 500Ω  
RP = 200Ω  
CA = 280pF  
CB = 45pF  
LA = 10µH  
256Ω  
22nF  
256Ω  
22nF  
2kΩ  
2kΩ  
20kΩ  
20kΩ  
AVDD  
RA  
AD976x  
AD8346  
I
= 11mA  
RL  
RB  
OUTFS  
AVDD = 5.0V  
VCM = 1.2V  
NOTES  
1. DAC FULL-SCALE OUTPUT CURRENT = I  
V
MOD  
.
OUTFS  
2. RA, RB, AND RL ARE THIN FILM RESISTOR NETWORKS  
WITH 0.1% MATCHING, 1% ACCURACY AVAILABLE  
FROM OHMTEK ORNXXXXD SERIES OR EQUIVALENT.  
0 TO I  
OUTFS  
V
DAC  
Figure 84. Baseband QAM Implementation Using an AD9763 and an AD8346  
Rev. G | Page 32 of 44  
 
 
 
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