參數(shù)資料
型號: ADS6224IRGZ25
廠商: TEXAS INSTRUMENTS INC
元件分類: ADC
英文描述: 2-CH 12-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQCC48
封裝: 7 X 7 MM, GREEN, PLASTIC, VQFN-48
文件頁數(shù): 40/73頁
文件大?。?/td> 3182K
代理商: ADS6224IRGZ25
www.ti.com
Using Differential Amplifier Drive Circuits
R
G
R
F
R
F
R
FIL
R
FIL
C
FIL
C
FIL
R
G
0.1 F
m
0.1 F
m
0.1 F
m
0.1 F
m
0.1 F
m
0.1 F
m
0.1 F
m
10 F
m
10 F
m
R
S
R
S
T
||R
R
T
+V
S
CM
INP
INM
ADS6xxx
THS4509
VCM
500 W
200 W
5 W
500 W
0.1 F
m
–V
S
S0259-01
INPUT COMMON MODE
155 mAxFs
125 MSPS
(1)
REFERENCE
SLAS543A – MAY 2007 – REVISED SEPTEMBER 2007
Figure 84 shows a drive ciruit using a differential amplifier (TI's THS4509) to convert a single-ended input to
differential output that can be interfaced to the ADC input pins. In addition to the single-ended to differential
conversion, the amplifier also provides gain (10 dB in Figure 84). As shown in the figure, RFIL helps to isolate the
amplifier output from the switching inputs of the ADC. Together with CFIL, it also forms a low-pass filter that
bandlimits the noise (and signal) at the ADC input. As the amplifier outputs are ac-coupled, the common-mode of
the ADC input pins is set using two resistors connected to VCM. The amplifier outputs can also be dc-coupled.
Using the output common-mode control of the THS4509, the ADC input pins can be biased to 1.5 V.
Figure 84. Drive Circuit using THS4509
Refer to the EVM User Guide (SLAU196) for more information.
To ensure a low-noise common-mode reference, the VCM pin is filtered with a 0.1-
μF low-inductance capacitor
connected to ground. The VCM pin is designed to directly drive the ADC inputs. The input stage of the ADC
sinks a common-mode current in the order of 155
μA at 125 MSPS (per input pin). Equation 1 describes the
dependency of the common-mode current and the sampling frequency.
This equation helps to design the output capability and impedance of the CM driving circuit accordingly.
The ADS622X has built-in internal references REFP and REFM, requiring no external components. Design
schemes are used to linearize the converter load seen by the references; this and the on-chip integration of the
requisite reference capacitors eliminates the need for external decoupling. The full-scale input range of the
converter can be controlled in the external reference mode as explained below. The internal or external reference
modes can be selected by programming the register bit <REF> (Table 14).
Copyright 2007, Texas Instruments Incorporated
45
Product Folder Link(s): ADS6225 ADS6224 ADS6223 ADS6222
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