LT1223 Linear Technology, LT1223 Datasheet - Page 6

• Manufacturer Part Number: LT1223
• Description: 100MHz Current Feedback Amplifier
• Manufacturer: Linear Technology

LT1223
TYPICAL PERFOR
A
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
works with internal junction capacitances of the LT1223 to
set the closed-loop bandwidth.
Even though the gain set resistor (R
to ground works with R
6
PPLICATI
–10
–15
–20
–25
–30
–10
20
15
10
–5
10
–2
–4
–6
–8
5
0
8
6
4
2
0
1M
Voltage Gain and Phase vs
Frequency
Noninverting Amplifier Settling
Time to 10mV vs Output Step
0
A = +1
R
V = 15V
R = 1k
S
V
F
L
PHASE
= 1k
GAIN
20
R = 100
L
10M
SETTLING TIME (ns)
FREQUENCY (Hz)
O
40
R = 100
L
R
U
L
F
TO 10mV
S
TO 10mV
) from output to inverting input
60
1k
F
100M
to set the voltage gain just like it
V = 15V
R
I FOR ATIO
R
S
F
U
L
W
= R
LT1223 • TPC20
80
LT1223 • TPC23
G
1k
= 1k
A
U
100
1G
G
CE
) from inverting input
180
135
225
90
45
0
–45
–90
–135
–180
–225
W
C
HARA TERISTICS
0.001
0.01
–10
0.1
10
–2
–4
–6
–8
8
6
4
2
0
10
U
Total Harmonic Distortion vs
Frequency
Noninverting Amplifier Settling
Time to 1mV vs Output Step
0
V = 15V
V = 7V
R = 400
R
A = +1
R = 1k
V = 15V
R = 1k
S
O
L
F
S
V
F
L
= R
C
G
RMS
100
=1k
SETTLING TIME ( s)
FREQUENCY (Hz)
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
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.
1k
1
THD
TO 1mV
TO 1mV
10k
LT1223 • TPC21
LT1223 • TPC24
F
constant and changing the gain with R
100k
2
–20
–30
–40
–50
–60
–70
–10
10
–2
–4
–6
–8
8
6
4
2
0
2nd and 3rd Harmonic
Distortion vs Frequency
1
Inverting Amplifier Settling
Time vs Output Step
0
A = –1
R = 1k
V = 15V
R = 1k
V = 15V
V = 2V
R = 100
R
A = 10dB
F
S
L
V
S
O
F
V
L
TO 10mV
= 1k
20
P-P
SETTLING TIME (ns)
FREQUENCY (MHz)
TO 10mV
40
10
TO 1mV
60
TO 1mV
3RD
2ND
LT1223 • TPC22
LT1223 • TPC25
80
G
, the
100
100