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參數(shù)資料
| 型號： | AD9114-DPG2-EBZ |
| 廠商： | Analog Devices Inc |
| 文件頁數(shù)： | 46/52頁 |
| 文件大?。?/td> | 0K |
| 描述： | IC DAC DUAL 8BIT LO PWR 40LFCSP |
| 標準包裝： | 1 |
| 系列： | TxDAC® |
| DAC 的數(shù)量： | 2 |
| 位數(shù)： | 8 |
| 采樣率（每秒）： | 125M |
| 數(shù)據(jù)接口： | 串行 |
| DAC 型： | 電流 |
| 工作溫度： | -40°C ~ 85°C |
| 已供物品： | 板 |
| 已用 IC / 零件： | AD9114 |
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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
–5
–15
–25
–35
–45
–55
–65
–75
–85
–95
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
447.5
449.0
450.0
451.0
452.5
FREQUENCY (MHz)
dB
07466-
070
Figure 109. AD9114/AD9115/AD9116/AD9117 and ADL5370 with a Single-
Tone Signal at 450 MHz, No Gain or LO Compensation
5
–5
–15
–25
–35
–45
–55
–65
–75
–85
–95
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
447.5
449.0
450.0
451.0
452.5
FREQUENCY (MHz)
dB
07466-
071
Figure 110. AD9114/AD9115/AD9116/AD9117 and ADL5370 with a Single-
Tone Signal at 450 MHz, Gain and LO Compensation Optimized
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