TSA1005-20IF View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
TSA1005-20IF Datasheet PDF : 22 Pages
| |||
TSA1005
External reference and common mode
Each of the voltages VREFP and INCM can be
fixed externally to better fit to the application
needs (Refer to table ’OPERATING
CONDITIONS’ page 4 for min/max values).
The VREFP, VREFM voltages set the analog
dynamic at the input of the converter that has a full
scale amplitude of 2*(VREFP-VREFM). Using
internal references, the dynamic range is 1.8V.
The INCM is the mid voltage of the analog input
signal.
It is possible to use an external reference voltage
device for specific applications requiring even
better linearity, accuracy or enhanced
temperature behavior.
Using the STMicroelectronics TS821 or
TS4041-1.2 Vref leads to optimum performances
when configured as shown on Figure 2.
Figure 2: External reference setting
1:4) to reduce the driving requirement on the
analog signal source.
Each analog input can drive a 1.4Vpp amplitude
input signal, so the resultant differential amplitude
is 2.8Vpp.
Figure 3: Differential input configuration with
transformer
Analog source
ADT1-1
1:1
VIN
TSA1005
50Ω
33pF
I or Q ch.
VINB
INCM
330pF
10nF 470nF
1kΩ
VCCA VREFP
VIN
TSA1005
VINB
VREFM
330pF 10nF 4.7uF
TS821
TS4041
external
reference
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 4: AC-coupled differential input
DRIVING THE DIFFERENTIAL ANALOG
INPUTS
The TSA1005 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. 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
0.46V. It determines the DC component of the
analog signal. As being an high impedance input,
it acts as an I/O and can be externally driven to
adjust this DC component. 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
50Ω
common
mode
10nF
33pF
50Ω 10nF
100kΩ
100kΩ
VIN
INCM TSA1005
VINB
Figure 5: AC-coupled Single-ended input
Signal source
10nF
50Ω
33pF
100kΩ
100kΩ
VIN
INCM TSA1005
VINB
15/22
Share Link: 