參數(shù)資料
型號: AD7942BCPRL7
廠商: ANALOG DEVICES INC
元件分類: ADC
英文描述: 14-Bit, 250 kSPS PulSAR ADC in MSOP/QFN
中文描述: 1-CH 14-BIT SUCCESSIVE APPROXIMATION ADC, SERIAL ACCESS, DSO10
封裝: 3 X 3 MM, QFN-10
文件頁數(shù): 8/28頁
文件大?。?/td> 633K
代理商: AD7942BCPRL7
AD7942
Preliminary Technical Data
Rev Pr B | Page 16 of 28
Driver Amplifier Choice
Although the AD7942 is easy to drive, the driver amplifier
needs to meet the following requirements:
The noise generated by the driver amplifier needs to be
kept as low as possible in order to preserve the SNR and
transition noise performance of the AD7942. Note that the
AD7942 has a noise much lower than most of the other 14-
bit ADCs and, therefore, can be driven by a noisier op amp
while preserving the same or better system performance.
The noise coming from the driver is filtered by the AD7942
analog input circuit 1-pole, low-pass filter made by R1 and
C2 or by the external filter, if one is used.
For ac applications, the driver needs to have a THD
performance suitable to that of the AD7942. Figure 12
gives the THD versus frequency that the driver should
exceed.
For multichannel multiplexed applications, the driver
amplifier and the AD7942 analog input circuit must be able
to settle for a full-scale step of the capacitor array at a 14-
bit level (0.006%). In the amplifier’s data sheet, settling at
0.1% to 0.01% is more commonly specified. This could
differ significantly from the settling time at a 14-bit level
and should be verified prior to driver selection.
Table 9. Recommended Driver Amplifiers.
Amplifier
Typical Application
Very low noise and high frequency
Low noise and high frequency
Low power, low noise, and low frequency
5 V single-supply, low power
Small, low power and low frequency
High frequency and low power
Voltage Reference Input
The AD7942 voltage reference input, REF, has a dynamic input
impedance and should therefore be driven by a low impedance
source with efficient decoupling between the REF and GND
pins as explained in the Layout section.
When REF is driven by a very low impedance source, e.g., a
reference buffer using the AD8031 or the AD8605, a 10 F
(X5R, 0805 size) ceramic chip capacitor is appropriate for
optimum performance.
If an unbuffered reference voltage is used, the decoupling value
depends on the reference used. For instance, a 22 F (X5R, 1206
size) ceramic chip capacitor is appropriate for optimum
performance using a low temperature drift ADR43x reference.
If desired, smaller reference decoupling capacitor values down
to 2.2 F can be used with a minimal impact on performance,
especially DNL.
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