coupled circuit. Transformers with turn ratios " />
參數(shù)資料
型號(hào): AD9877ABSZ
廠商: Analog Devices Inc
文件頁數(shù): 26/36頁
文件大?。?/td> 0K
描述: IC PROCESSOR FRONT END 100MQFP
標(biāo)準(zhǔn)包裝: 1
位數(shù): 12
通道數(shù): 3
功率(瓦特): 1.17W
電壓 - 電源,模擬: 3.3V
電壓 - 電源,數(shù)字: 3.3V
封裝/外殼: 100-BQFP
供應(yīng)商設(shè)備封裝: 100-MQFP(14x20)
包裝: 托盤
AD9877
Rev. B | Page 32 of 36
Figure 43 shows the schematic of a possible transformer
coupled circuit. Transformers with turn ratios (n2/n1) other than
1 can be selected to optimize the performance of a given
application. For example, selecting a transformer with a higher
impedance ratio (such as minicircuits T16 to 6T with an
impedance ratio of (z2/z1) = 16 = (n2/n1)2) effectively steps up
the signal amplitude, thus further reducing the output voltage
swing of the signal source.
AINP
AINN
AD9877
R
R1
C
02716-043
Figure 43. Transformer Coupled Input
In Figure 43, a resistor R1 is added between the analog inputs to
match the source impedance R as in the formula
R = [R1||RAIN](Z1/Z2)
ADC VOLTAGE REFERENCES
The AD9877 has two independent internal references for its
8-bit and 12-bit ADCs. Both 8-bit ADCs have a 1 V p-p input
and share one internal reference source. The 12-bit ADC,
however, is designed for 2 V p-p input voltages and provides its
own internal reference. Figure 16 shows the proper connections
of the reference pins REFT and REFB.
External references may be necessary for systems that require
high accuracy gain matching between ADCs or improvements
in temperature drift and noise characteristics. External
references REFT and REFB need to be centered at AVDD/2
with offset voltages as specified:
REFT8: AVDDIQ/2 + 0.25 V
REFB8: AVDDIQ/2 0.25 V
REFT12: AVDD/2 + 0.5 V
REFB12: AVDD/2 0.5 V
A differential level of 0.5 V between the reference pins results in
a 1 V p-p ADC input level AIN. A differential level of 1 V
between the reference pins results in a 2 V p-p ADC input level
AIN. Internal reference sources can be powered down when
external references are used (Register Address 0x002).
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