TAMC900-A1 User Manual Issue 1.0.2
Page 10 of 17
4.2
Single Ended Signal Source
If a single ended signal source is used, it can be connected to the TAMC900-A1 in the following way:
- +
+ -
3.3 Volt
R
I
R
I
R
F
LTC6404
-IN
+IN
LTC2254
ANALOG_IN-
AN
GND
GND
GND
R
F
ADC
(TAMC900)
TAMC900-A1
Single Ended
Signal Source
Figure 4-2 : Single Ended Signal Source
In the above configuration, ANALOG_IN- should not exceed ±1.0 Volt (ADC input voltage range).
Unfortunately, most signal sources have a non-zero output impedance R
S
. This causes feedback
imbalance between the pair of feedback networks. For the best performance, it is recommended that
the input source output impedance be compensated for. If input impedance matching is required by
the source, a termination resistor R
T
should be chosen:
S
S
R
R
−
Ω
×
T
R
Ω
=
200
200
(200
Ω
is the input impedance of ANALOG_IN-)
To provide differential balance, R
DB
is chosen to equal R
T
|| R
S
:
S
T
S
T
DB
R
R
R
R
R
+
=
- +
+ -
3.3 Volt
R
I
R
I
R
F
R
F
LTC6404
-IN
+IN
LTC2254
ADC
(TAMC900)
TAMC900-A1
ANALOG_IN-
AN
GND
R
T
Single Ended
Signal Source
GND
GND
R
DB
R
S
Figure 4-3 : Single Ended Signal Source with impedance matching
The overall single-ended to differential gain (GAIN
SE
) must take into account the input attenuation
of the R
S
and R
T
resistive divider and the effect of adding R
DB
:
)
150
(
)
)
(
150
)(
300
(
DB
T
S
S
T
S
DB
SE
R
R
R
R
R
R
GAIN
+
T
R
R
−
+
+
=
