AD9714-DPG2-EBZ (Analog) PDF资料下载 Datasheet(47/80 页)

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参数资料

型号：	AD9714-DPG2-EBZ
厂商：	Analog Devices Inc
文件页数：	47/80页
文件大小：	0K
描述：	ADC 8BIT DUAL 40LFCSP
标准包装：	1
系列：	TxDAC®
DAC 的数量：	2
位数：	8
采样率（每秒）：	125M
数据接口：	串行
DAC 型：	电流
工作温度：	-40°C ~ 85°C
已供物品：	板
已用 IC / 零件：	AD9714

AD9714/AD9715/AD9716/AD9717

Rev. A | Page 51 of 80

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

100 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

AD9714/AD9715/AD9716/AD9717 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 110

and Figure 111. Figure 110 shows the output spectrum of the

quadrature demodulator before gain and offset correction.

Figure 111 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 correc-

tion, 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 depen-

dent; therefore, routines must be developed to adjust it if

wideband signals are desired.

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447.5

449.0

450.0

451.0

452.5

FREQUENCY (MHz)

)

Figure 110. AD9714/AD9715/AD9716/AD9717 and ADL5370 with a Single-

Tone Signal at 450 MHz, No Gain or LO Compensation

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