Datasheet

LTC6910-1
LTC6910-2/LTC6910-3
21
6910123fa
TYPICAL APPLICATIO
U
Figure 7 shows a block diagram and Figure 8 the practical
circuit for a low noise amplifier with gain and bandwidth
independently programmable over 100:1 ranges. One
LTC6910-X controls the gain and another controls the
bandwidth. An LT1884 dual op amp forms an integrating
lowpass loop with capacitor C2 to set the programmable
upper corner frequency. The LT1884 also supports rail-to-
rail output swings over the total supply voltage range of
2.7V to 10.5V. AC coupling through capacitor C1 estab-
–
+
–
+
–
+
–
+
V
IN
C1
GAIN CONTROL PGA
(GAIN A)
V
OUT
= (GAIN A)V
IN
BANDWIDTH CONTROL PGA
(GAIN B)
GAIN = –1
C2
R1
R2
V
OUT
6910 F05
1
2πR1C1
≤ BANDWIDTH ≤
1
R2
(GAIN B)
2π C2
Figure 7. Block Diagram of an AC Amplifier with Programmable Gain and Bandwidth
lishes a fixed low frequency corner of 1Hz, which can be
adjusted by changing C1. Alternatively, shorting C1 makes
the amplifier DC coupled. (If DC gain is not needed,
however, the AC coupling suppresses several error sources:
any shifts in DC levels, low frequency noise and all
amplifier DC offset voltages other than the low internally
trimmed LT1884 offset in the integrating amplifier. If
desired, another coupling capacitor in series with the input
can relax the requirements on DC input level as well.)