ltc6404cud-2-trpbf Linear Technology Corporation, ltc6404cud-2-trpbf Datasheet - Page 18

• Manufacturer Part Number: ltc6404cud-2-trpbf
• Description: 600mhz, Low Noise, Ac Precision Fully Differential Input/output Ampli?er/driver
• Manufacturer: Linear Technology Corporation

APPLICATIONS INFORMATION
LTC6404-1
the output common mode voltage, resistor mismatch can
make the apparent voltage offset of the amplifi er appear
worse than specifi ed.
In general, the apparent input referred offset induced by
feedback factor mismatch is given by the equation:
where
Interfacing the LTC6404-1 to A/D Converters
The LTC6404-1’s rail-to-rail output and fast settling time
make the LTC6404-1 ideal for interfacing to low voltage,
single supply, differential input ADCs. The sampling process
of ADCs create a sampling glitch caused by switching in the
sampling capacitor on the ADC front end which momentarily
“shorts” the output of the amplifi er as charge is transferred
between the amplifi er and the sampling cap. The amplifi er
must recover and settle from this load transient before this
acquisition period ends for a valid representation of the
input signal. In general, the LTC6404-1 will settle much
18
V
Δβ =
OSDIFF(APPARENT)
3.3V
0.1μF
0.1μF
R
I
2
R
+
I
2
R
V
IN
F
, 2V
2
1
2
3
4
–
SHDN
V
V
V
P-P
+
–
OCM
R
≈ (V
16
V
V
5
I
SHDN
+
–
1
R
100Ω
100Ω
+
NC
NC
I
INCM
1
R
F
15
6
1
Figure 11. Interfacing the LTC6404-1 to a High Speed 105Msps ADC
– V
IN
IN
100Ω
100Ω
+
–
V
+
–
OCM
OCM
14
7
) • Δβ
OUT
OUT
–
+
13
8
OUTF
OUTF
LTC6404-1
V
+
–
+
V
V
–
–
64041 F11
V
V
V
V
–
+
+
–
12
11
10
9
more quickly from these periodic load impulses than from a
2V input step, but it is a good idea to either use the fi ltered
outputs to drive the ADC (Figure 11 shows an example
of this), or to place a discrete R-C fi lter network between
the differential unfi ltered outputs of the LTC6404-1 and
the input of the ADC to help absorb the charge transfer
required during the ADC sampling process. The capaci-
tance of the fi lter network serves as a charge reservoir
to provide high frequency charging during the sampling
process, while the two resistors of the fi lter network are
used to dampen and attenuate any charge kickback from
the ADC. The selection of the R-C time constant is trial
and error for a given ADC, but the following guidelines
are recommended: Choosing too large of a resistor in the
decoupling network (leaving insuffi cient settling time) will
create a voltage divider between the dynamic input imped-
ance of the ADC and the decoupling resistors. Choosing
too small of a resistor will possibly prevent the resistor
from properly damping the load transient caused by the
sampling process, prolonging the time required for set-
tling. 16-bit applications typically require a minimum of 11
R-C time constants. It is recommended that the capacitor
chosen have a high quality dielectric (for example, C0G
multilayer ceramic).
0.1μF
0.1μF
3.3V
V
2.2μF
CM
AIN
AIN
+
–
LTC2207
GND
CONTROL
V
DD
D15
D0
•
•
1μF
1μF
3.3V
64041f