Datasheet

LT1223
7
1223fb
APPLICATIO S I FOR ATIO
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TYPICAL PERFOR A CE CHARACTERISTICS
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does in a voltage feedback op amp, the closed-loop
bandwidth does not change. This is because the equiva-
lent gain bandwidth product of the current feedback am-
plifier is set by the Thevenin equivalent resistance at the
inverting input and the internal compensation capacitor.
By keeping R
F
constant and changing the gain with R
G
, the
Thevenin resistance changes by the same amount as the
change in gain. As a result, the net closed-loop bandwidth
of the LT1223 remains the same for various closed-loop
gains.
Voltage Gain and Phase vs Total Harmonic Distortion vs 2nd and 3rd Harmonic
Frequency Frequency Distortion vs Frequency
Noninverting Amplifier Settling Noninverting Amplifier Settling Inverting Amplifier Settling
Time to 10mV vs Output Step Time to 1mV vs Output Step Time vs Output Step
Current Feedback Basics
The small-signal bandwidth of the LT1223, like all current
feedback amplifiers, isn’t a straight inverse function of the
closed-loop gain. This is because the feedback resistors
determine the amount of current driving the amplifier’s
internal compensation capacitor. In fact, the amplifier’s
feedback resistor (R
F
) from output to inverting input
works with internal junction capacitances of the LT1223 to
set the closed-loop bandwidth.
Even though the gain set resistor (R
G
) from inverting input
to ground works with R
F
to set the voltage gain just like it
FREQUENCY (Hz)
1M
–30
VOLTAGE GAIN (dB)
–15
5
20
10M 100M 1G
LT1223 • TPC20
R 1k
L
GAIN
–25
–20
–10
–5
0
10
15
PHASE SHIFT (DEGREES)
–225
–90
90
225
–180
–135
–45
0
45
135
180
PHASE
≥
R = 100
L
Ω
R 1k
L
≥
R = 100
L
Ω
V = 15V
R
F
= R
G
= 1k
S
±
FREQUENCY (Hz)
TOTAL HARMONIC DISTORTION (%)
0.01
0.1
10 1k 10k 100k
LT1223 • TPC21
0.001
100
THD
V = 15V
V = 7V
R = 400
R
F
= R
G
=1k
S
O
L
±
RMS
Ω
FREQUENCY (MHz)
1
–70
DISTORTION (dBc)
–20
10 100
LT1223 • TPC22
–60
–50
–40
–30
2ND
3RD
V = 15V
V = 2V
P-P
R = 100
R
F
= 1k
A = 10dB
S
±
O
L
V
SETTLING TIME (ns)
0
–10
OUTPUT STEP (V)
–4
10
LT1223 • TPC23
20 40 60 80 100
–8
–6
–2
0
2
4
6
8
TO 10mV
TO 10mV
V
S
L
±
A = +1
R
F
= 1k
V = 15V
R = 1k
SETTLING TIME ( s)
0
–10
OUTPUT STEP (V)
–4
10
LT1223 • TPC24
12
–8
–6
–2
0
2
4
6
8
TO 1mV
µ
TO 1mV
A = +1
R = 1k
V = 15V
R = 1k
F
S
±
V
L
SETTLING TIME (ns)
0
–10
OUTPUT STEP (V)
–4
10
LT1223 • TPC25
100
–8
–6
–2
0
2
4
6
8
TO 1mV
TO 10mV
A = –1
R = 1k
V = 15V
R = 1k
F
S
±
V
20 40 60 80
L
TO 10mV
TO 1mV