AD9117BCPZ (Analog) PDF资料下载 Datasheet(46/52 页)

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参数资料

型号：	AD9117BCPZ
厂商：	Analog Devices Inc
文件页数：	46/52页
文件大小：	0K
描述：	IC DAC DUAL 14BIT LO PWR 40LFCSP
产品培训模块：	Data Converter Fundamentals DAC Architectures
设计资源：	High CMRR Circuit for Converting Wideband Complementary DAC Outputs to Single-Ended Without Precision Resistors (CN0142)
标准包装：	1
系列：	TxDAC®
位数：	14
数据接口：	串行
转换器数目：	2
电压电源：	模拟和数字
功率耗散（最大）：	232mW
工作温度：	-40°C ~ 85°C
安装类型：	表面贴装
封装/外壳：	40-VFQFN 裸露焊盘，CSP
供应商设备封装：	40-LFCSP-VQ（6x6）
包装：	托盘
输出数目和类型：	4 电流，单极
采样率（每秒）：	125M
产品目录页面：	785 (CN2011-ZH PDF)

AD9114/AD9115/AD9116/AD9117

Data Sheet

Rev. C | Page 50 of 52

Note that LO feedthrough compensation is independent of

phase compensation. However, gain compensation can affect

the LO compensation because the gain compensation may change

the common-mode level of the signal. The dc offset of some

modulators is common-mode level dependent. Therefore, it is

recommended that the gain adjustment be performed prior to

LO compensation.

LO FEEDTHROUGH COMPENSATION

To achieve LO feedthrough compensation in a circuit, each

output of the two AUXDACs must be connected through a

10 kΩ resistor to one side of the differential DAC output. See

the Auxiliary DACs section for details of how to use AUXDACs.

The purpose of these connections is to drive a very small amount

of current into the nodes at the quadrature modulator inputs,

thereby adding a slight dc bias to one or the other of the

quadrature modulator signal inputs.

To achieve LO feedthrough compensation, the user should start

with the default conditions of the AUXDAC registers and then

increment the magnitude of one or the other AUXDAC output

voltages. While this is being done, the amplitude of the LO

feedthrough at the quadrature modulator output should be

sensed. If the LO feedthrough amplitude increases, try either

decreasing the output voltage of the AUXDAC being adjusted

or try adjusting the output voltage of the other AUXDAC. It

may take practice before an effective algorithm is achieved. The

AD9114/AD9115/AD9116/ AD9117 evaluation board can be

used to adjust the LO feedthrough down to the noise floor,

although this is not stable over temperature.

RESULTS OF GAIN AND OFFSET CORRECTION

The results of gain and offset correction can be seen in Figure 109

and Figure 110. Figure 109 shows the output spectrum of the

quadrature demodulator before gain and offset correction.

Figure 110 shows the output spectrum after correction. The

LO feedthrough spur at 450 MHz has been suppressed to the

noise level. This result can be achieved by applying the correction,

but the correction must be repeated after a large change in

temperature.

Note that gain matching improves the negative frequency

image rejection, but it is also related to the phase mismatch in

the quadrature modulator. It can be improved by adjusting the

relative phase between the two quadrature signals at the digital side

or properly designing the low-pass filter between the DACs and

quadrature modulators. Phase mismatch is frequency dependent;

therefore, routines must be developed to adjust it if wideband

signals are desired.

–5

–15

–25

–35

–45

–55

–65

–75

–85

–95

–10

–20

–30

–40

–50

–60

–70

–80

–90

447.5

449.0

450.0

451.0

452.5

FREQUENCY (MHz)

07466-

070

Figure 109. AD9114/AD9115/AD9116/AD9117 and ADL5370 with a Single-

Tone Signal at 450 MHz, No Gain or LO Compensation

–5