參數(shù)資料
型號: TSA0801IFT
廠商: STMICROELECTRONICS
元件分類: ADC
英文描述: 1-CH 8-BIT PROPRIETARY METHOD ADC, PARALLEL ACCESS, PQFP48
封裝: 7 X 7 MM, PLASTIC, TQFP-48
文件頁數(shù): 7/21頁
文件大?。?/td> 0K
代理商: TSA0801IFT
TSA0801
15/21
NO
T
FOR
NEW
DESI
G
N
DRIVING THE ANALOG INPUT
Differential inputs
The TSA0801 has been designed to obtain
optimum performances when being differentially
driven. An RF transformer is a good way to
achieve such performances. Figure 3 describes
the schematics. The input signal is fed to the
primary of the transformer, while the secondary
drives both ADC inputs.
Figure 3 : Differential input configuration with
transformer
The common mode voltage of the ADC (INCM) is
connected to the center-tap of the secondary of
the transformer in order to bias the input signal
around this common voltage, internally set to
0.57V. The INCM is decoupled to maintain a low
noise level on this node. Our evaluation board is
mounted with a 1:1 ADT1-1WT transformer from
Minicircuits.
You
might
also
use
a
higher
impedance ratio (1:2 or 1:4) to reduce the driving
requirement on the analog signal source. For
example, with internal references, each analog
input can drive a 1Vpp amplitude input signal, so
the resultant differential amplitude is 2Vpp.
Figure 4 : AC-coupled differential input
Figure 4 represents the biasing of a differential
input signal in AC-coupled differential input
configuration. Both inputs VIN and VINB are
centered around the common mode voltage, that
can be let internal or fixed externally.
Figure 5 shows a DC-coupled configuration with
forced INCM to the DC analog input (mid-voltage)
while VREFM is connected to ground and
VFREFP let internal (to 1V); we achieve a 2Vpp
differential amplitude.
Figure 5 : DC-coupled 2Vpp differential analog
input
Single-ended input configuration
The single-ended input configuration of the
TSA0801 requires particular biasing and driving.
The structure being fully differential, care has to
be taken in order to properly bias the inputs in sin-
gle-ended mode. Figure 6 summarizes the link
from the differential configuration to the sin-
gle-ended one; a wrong configuration is also pre-
sented.
- With differential driving, both inputs are centered
around the INCM voltage.
- The transition to single-ended configuration
implies to connect the unused input (VINB for
instance) to the DC component of the single input
(VIN) and also to the input common mode in order
to be well balanced. The mid-code is achieved at
the crossing between VIN and VINB, therefore
inputs are conveniently biased.
- Unlikely other structures of converters in which
the unused channel can be grounded; in our case
it will end with unbalanced inputs and saturation of
the internal amplifiers leading to a non respect of
the output codes.
TSA0801
VIN
VINB
INCM
50
100pF
330pF
4.7uF
10nF
Analog source
1:1
ADT1-1
50
10nF
TSA0801
VIN
VINB
INCM
33pF
100k
100k
50
10nF
common
mode
TSA0801
VIN
VINB
INCM
330pF
4.7uF
10nF
analog
DC
AC+DC
VREFP
VREFM
VREFP-VREFM = 1 V
DC
analog
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