LTC2241-12 Linear Technology, LTC2241-12 Datasheet - Page 17

• Manufacturer Part Number: LTC2241-12
• Description: 210Msps ADC
• Manufacturer: Linear Technology

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APPLICATIO S I FOR ATIO
sample-and-hold charging glitches and limiting the
wideband noise at the converter input. For input frequen-
cies higher than 100MHz, the capacitor may need to be
decreased to prevent excessive signal loss.
The A
package inductance. The two A
should be shorted together.
For input frequencies above 100MHz the input circuits of
Figure 6, 7 and 8 are recommended. The balun transformer
gives better high frequency response than a flux coupled
center-tapped transformer. The coupling capacitors allow
the analog inputs to be DC biased at 1.25V. In Figure 8 the
series inductors are impedance matching elements that
maximize the ADC bandwidth.
Reference Operation
Figure 9 shows the LTC2241-12 reference circuitry con-
sisting of a 1.25V bandgap reference, a difference ampli-
fier and switching and control circuit. The internal voltage
reference can be configured for two pin selectable input
ranges of 2V (±1V differential) or 1V (±0.5V differential).
Tying the SENSE pin to V
the SENSE pin to V
The 1.25V bandgap reference serves two functions: its
output provides a DC bias point for setting the common
mode voltage of any external input circuitry; additionally,
the reference is used with a difference amplifier to gener-
ate the differential reference levels needed by the internal
ADC circuitry. An external bypass capacitor is required for
the 1.25V reference output, V
frequency low impedance path to ground for internal and
external circuitry.
The difference amplifier generates the high and low refer-
ence for the ADC. High speed switching circuits are
connected to these outputs and they must be externally
bypassed. Each output has four pins: two each of REFHA
and REFHB for the high reference and two each of REFLA
and REFLB for the low reference. The multiple output pins
are needed to reduce package inductance. Bypass capaci-
tors must be connected as shown in Figure 9.
IN
+
and A
IN
–
inputs each have two pins to reduce
U
CM
selects the 1V range.
U
DD
selects the 2V range; typing
CM
IN
+
. This provides a high
W
and the two A
U
IN
–
pins
ANALOG
ANALOG
ANALOG
INPUT
INPUT
INPUT
Figure 6. Recommended Front End Circuit for
Input Frequencies Between 100MHz and 250MHz
Figure 7. Recommended Front End Circuit for
Input Frequencies Between 250MHz and 500MHz
Figure 8. Recommended Front End Circuit for
Input Frequencies Above 500MHz
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
0.1µF
T1 = MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1 = MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1 = MA/COM ETC1-1-13
RESISTORS, CAPACITORS
ARE 0402 PACKAGE SIZE
T1
T1
T1
25Ω
25Ω
25Ω
25Ω
25Ω
25Ω
2.7nH
0.1µF
0.1µF
0.1µF
10Ω
12Ω
12Ω
2.7nH
10Ω
10Ω
LTC2241-12
2.2µF
2.2µF
8pF
2.2µF
V
A
A
A
A
V
A
A
A
A
V
A
A
A
A
CM
IN
IN
IN
IN
CM
IN
IN
IN
IN
CM
IN
IN
IN
IN
+
+
–
–
+
+
–
–
+
+
–
–
LTC2241-12
LTC2241-12
LTC2241-12
224112 F08
17
224112 F06
224112 F07
224112fa