lt1810 Linear Technology Corporation, lt1810 Datasheet - Page 18

• Manufacturer Part Number: lt1810
• Description: Single/dual 180mhz, 350v/?s Rail-to-rail Input And Output Low Distortion Op Amps
• Manufacturer: Linear Technology Corporation

LT1809/LT1810
Driving A/D Converters
The LT1809/LT1810 have a 27ns settling time to 0.1% of
a 2V step signal and 20 output impedance at 100MHz
making it ideal for driving high speed A/D converters. With
the rail-to-rail input and output and low supply voltage
operation, the LT1809 is also desirable for single supply
applications. As shown in Figure 2, the LT1809 drives a
10Msps, 12-bit ADC, the LTC1420. The lowpass filter, R3
and C1, reduces the noise and distortion products that
might come from the input signal. High quality capacitors
TYPICAL APPLICATIO S
18
1V
V
P-P
IN
U
R1
1k
+
–
LT1809
–100
–120
–20
–40
–60
–80
–5V
5V
0
Figure 3. 4096 Point FFT Response
0
Figure 2. Noninverting A/D Driver
R2
1k
1
49.9
R3
FREQUENCY (MHz)
2
C1
470pF
and resistors, an NPO chip capacitor and metal-film sur-
face mount resistors, should be used since these compo-
nents can add to distortion. The voltage glitch of the
converter, due to its sampling nature, is buffered by the
LT1809 and the ability of the amplifier to settle it quickly
will affect the spurious-free dynamic range of the system.
Figure 2 to Figure 7 depict the LT1809 driving the LTC1420
at different configurations and voltage supplies. The FFT
responses show better than 90dB of SFDR for a 5V
supply, and 80dB on a 5V single supply for the 1.394MHz
signal.
V
A
f
f
SFDR = 90dB
3
SAMPLE
IN
S
V
+A
= 5V
= +2
= 1.394MHz
–A
IN
IN
= 10Msps
4
PGA GAIN = 1
REF = 2.048V
LTC1420
1809 F03
–5V
5V
5
1809 F02
•
•
•
12 BITS
10Msps