LT1187M(Rev0) 데이터 시트보기 (PDF) - Linear Technology
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LT1187M Datasheet PDF : 12 Pages
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APPLICATIO S I FOR ATIO
Operating with Low Closed-Loop Gains
The LT1187 has been optimized for closed-loop gains of
2 or greater. For a closed-loop gain of 2 the response
peaks about 2dB. Peaking can be eliminated by placing a
capacitor across the feedback resistor, (feedback zero).
This peaking shows up as time domain overshoot of
about 25%.
LT1187
Small-Signal Transient Response
Closed-Loop Voltage Gain vs Frequency
9
8
7
CFB = 0pF
6
5
CFB = 5pF
4
3
CFB = 10pF
2
VS = ±5V
TA = 25°C
1 AV = 2
0
RFB = 900Ω
RG = 900Ω
–1
100k
1M
10M
FREQUENCY (Hz)
100M
LT1187 • AI03
Small-Signal Transient Response
AV = 2, OVERSHOOT = 25%, RFB = RG = 1k
LT1187 • AI04
AV = 2, WITH 8pF FEEDBACK CAPACITOR
LT1187 • AI05
Extending the Input Range
Figure 1 shows a simplified schematic of the LT1187. In
normal operation the REF pin 1 is grounded or taken to a
DC offset control voltage and differential signals are ap-
plied between pins 2 and 3. The input responds linearly
until all of the 345µA current flows through the 1.1k
resistor and Q1 (or Q2) turns off. Therefore the maximum
input swing is 380mVP or 760mVP-P. The second differen-
tial pair, Q3 and Q4, is running at slightly larger current so
that when the first input stage limits, the second stage
remains biased to maintain the feedback.
Occasionally it is necessary to handle signals larger than
760mVP-P at the input. The LT1187 input stage can be
tricked to handle up to 1.5VP-P. To do this, it is necessary
to ground pin 3 and apply the differential input signal
between pin 1 and 2. The input signal is now applied
across two 1.1k resistors in series. Since the input signal
is applied to both input pairs, the first pair will run out of
bias current before the second pair, causing the amplifier
to go open-loop. The results of this technique are shown
in the following scope photo.
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