LT1191 데이터 시트보기 (PDF) - Linear Technology

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LT1191

Ultrahigh Speed Operational Amplifier

Linear Technology 

LT1191

APPLICATIO S I FOR ATIO

Power Supply Bypassing

The LT1191 is quite tolerant of power supply bypassing. In

some applications a 0.1µF 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, RL = 1kΩ.

No Supply Bypass Capacitors

In most applications, and those requiring good settling

time, it is important to use multiple bypass capacitors. A

0.1µF ceramic disc in parallel with a 4.7µF 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 2.61µs for the

0.1µF bypass; the time drops to 143ns with multiple

bypass capacitors.

Settling Time Poor Bypass

AV = –1, IN DEMO BOARD, RL = 1kΩ

LT1191 • TA04

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.

VOUT

1V/DIV

0V

Closed-Loop Voltage Gain vs Frequency

20

VS = ±5V

TA = 25°C

RL = 1k

10

AV = 2

AV = 1

0

VOUT

1V/DIV

0V

0V

VOUT

1mV/DIV

SETTLING TIME TO 2mV, AV = –1

SUPPLY BYPASS CAPACITORS = 0.1µF

LT1191 • TA06

Settling Time Good Bypass

0V

VOUT

1mV/DIV

–10

–20

100k

1M

10M

100M

1G

FREQUENCY (Hz)

LT1191 • TA05

LT1191 • TA07

SETTLING TIME TO 2mV, AV = –1

SUPPLY BYPASS CAPACITORS = 0.1µF + 4.7µF TANTALUM

8

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