6

LT1223

CC

HARA TERISTICS

A

TYPICALPERFOR

CE

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.

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.

S

APPLICATI

I FOR ATIO

Voltage Gain and Phase vs

Total Harmonic Distortion vs

2nd and 3rd Harmonic

Frequency

Frequency

Distortion vs Frequency

FREQUENCY (Hz)

1M

–30

–15

5

20

10M

100M

1G

LT1223 • TPC20

R

1k

L

GAIN

–25

–20

–10

–5

0

10

15

–225

–90

90

225

–180

–135

–45

0

45

135

180

PHASE

≥

R = 100

L

Ω

R

1k

R = 100

L

Ω

V =

15V

S

±

FREQUENCY (Hz)

0.01

0.1

10

1k

10k

100k

LT1223 • TPC21

0.001

100

THD

V =

15V

V = 7V

R = 400

S

O

L

±

RMS

Ω

FREQUENCY (MHz)

1

–70

–20

10

100

LT1223 • TPC22

–60

–50

–40

–30

2ND

3RD

V =

15V

R = 100

A = 10dB

S

±

O

L

V

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

SETTLING TIME (ns)

0

–10

–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

V =

15V

R = 1k

SETTLING TIME ( s)

0

–10

–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

–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

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

works with internal junction capacitances of the LT1223 to

set the closed-loop bandwidth.