TMC1175A
PRODUCT SPECIFICATION
Typical Performance Characteristics
30
25
20
IDD (mA)
SFDR
15
10
5
0
0
10
20
30
40
60
50
40
30
20
10
0
0
2
4
6
fs = 20 Msps
fs = 30 Msps
fs = 40 Msps
8
10
12
Figure 8. Typical I
DD
vs f
S
Figure 9. Typical SFDR vs f
IN
and f
S
50
40
30
SNR
20
10
0
0
2
4
6
SNR
fs = 20 Msps
fs = 30 Msps
fs = 40 Msps
50
40
30
20
10
0
8
10
12
0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
fs = 20 Msps
fs = 33 Msps
Figure 10. Typical SNR vs f
IN
and f
S
Figure 11. Typical SNR vs Full Scale Input Range
Applications Discussion
The circuit in Figure 12 employs a band-gap reference to
generate a variable RT reference voltages for the
TMC1175A as well as a bias voltage to offset the wideband
input amplifier to mid-range. An "offset adjust"
is also shown for varying the mid-range voltage level.
The operational amplifier in the reference circuitry is a
standard 741-type.
The voltage reference at R
T
can be adjusted from 0.0 to 2.4
volts while R
B
is grounded. Diodes are used to restrict the
wideband amplifier output to between -0.7V and V
DD
+0.7V. Diode protection is good practice to limit the analog
input voltage at V
IN
to the safe operating range.
The circuit in Figure 13 shows self-bias of R
T
and R
B
by
connection to VR+ and VR-. This sets up a 0.6 to 2.6 Volt
input range for V
IN
. The input range is susceptible to power
supply variation since the voltages on R
T
and R
B
are directly
derived from V
DDA
. The video input is AC-coupled and
biased at a adjustable midpoint of the A/D input range.
This circuit offers the advantage of minimum support
circuitry for the most cost-sensitive applications.
In Figure 14, an external band-gap reference sets R
T
to +1.2
Volts while R
B
is grounded. The internal pull-up resistor,
R+, provides the bias current for the band-gap reference. The
A/D converter input is biased to the mid-point of the input
range.
12
REV. 1.3.3 2/28/02
CADEKA [ CADEKA MICROCIRCUITS LLC. ]
