LT1191 Linear Technology, LT1191 Datasheet - Page 8

• Manufacturer Part Number: LT1191
• Description: Ultra High Speed Operational Amplifier
• Manufacturer: Linear Technology

APPLICATIO S I FOR ATIO
Power Supply Bypassing
The LT1191 is quite tolerant of power supply bypassing. In
some applications a 0.1 F ceramic disc capacitor placed
1/2 inch from the amplifier is all that is required. A scope
photo of the amplifier output with no supply bypassing is
used to demonstrate this bypassing tolerance, R
LT1191
Supply bypassing can also affect the response in the
frequency domain. It is possible to see a slight rise in the
frequency response at 130MHz depending on the gain
configuration, supply bypass, inductance in the supply
leads and printed circuit board layout. This can be further
minimized by not using a socket.
8
Closed-Loop Voltage Gain vs Frequency
–10
–20
20
10
0
100k
V
T
R
No Supply Bypass Capacitors
A
S
L
= 5V
= 25 C
= 1k
A
V
= –1, IN DEMO BOARD, R
U
1M
A = 2
A = 1
FREQUENCY (Hz)
V
V
U
10M
100M
L
W
= 1k
LT1191 • TA05
LT1191 • TA04
1G
U
L
= 1k .
In most applications, and those requiring good settling
time, it is important to use multiple bypass capacitors. A
0.1 F ceramic disc in parallel with a 4.7 F tantalum is
recommended. Two oscilloscope photos with different
bypass conditions are used to illustrate the settling time
characteristics of the amplifier. Note that although the
output waveform looks acceptable at 1V/DIV, when ampli-
fied to1mV/DIV the settling time to 2mV is 2.61 s for the
0.1 F bypass; the time drops to 143ns with multiple
bypass capacitors.
1V/DIV
1V/DIV
V
V
OUT
OUT
0V
0V
SUPPLY BYPASS CAPACITORS = 0.1 F + 4.7 F TANTALUM
SUPPLY BYPASS CAPACITORS = 0.1 F
Settling Time Good Bypass
Settling Time Poor Bypass
SETTLING TIME TO 2mV, A
SETTLING TIME TO 2mV, A
V
V
= –1
= –1
LT1191 • TA06
LT1191 • TA07
0V
0V
V
1mV/DIV
V
1mV/DIV
OUT
OUT