LTC6605-7 Linear Technology, LTC6605-7 Datasheet - Page 17

• Manufacturer Part Number: LTC6605-7
• Description: Dual Matched 7MHz Filter
• Manufacturer: Linear Technology

APPLICATIONS INFORMATION
the sampling transient of the ADC (see Figure 8). The
capacitance serves to provide the bulk of the charge
during the sampling process, while the two resistors at
the outputs of the LTC6605-7 are used to dampen and
attenuate any charge injected by the ADC. The RC fi lter
gives the additional benefi t of band limiting broadband
output noise. The selection of the RC time constant is trial
and error for a given ADC, but the following guidelines are
recommended. Choose an RC time constant that is smaller
than the reciprocal of the fi lter cutoff frequency confi gured
by the LTC6605-7. Time constants on the order of 2ns
do a good job of fi ltering broadband noise. Longer time
V
IN
+
–
BIAS
1
2
3
4
5
1/2 LTC6605-7
–
+
CHANNEL A
22
21
20
19
18
0.1μF
10nF
Figure 8. Driving an ADC
1μF
3V
V
OCM
τ = R • (C1 + 2 • C2)
R
R
constants improve SNR at the expense of settling time.
The resistors in the decoupling network should be at least
25Ω. Too large of a resistor will leave insuffi cient settling
time. Too small of a resistor will not properly dampen the
load transient of the sampling process, prolonging the
time required for settling. In 16-bit applications, this will
typically require a minimum of eleven RC time constants.
The 10Ω resistors at the inputs to the ADC minimize the
sampling transients that charge the RC fi lter capacitors.
For lowest distortion, choose capacitors with low dielectric
absorption, such as a C0G multilayer ceramic capacitor.
C2
C1
C1
10Ω
10Ω
A
A
IN
IN
+
–
V
CM
ADC
2.2μF
CONTROL
GND
www.DataSheet4U.com
LTC6605-7
D15
D0
•
•
1μF
66057 F08
3.3V
17
66057f