OP467

REV. C

–13–

2.5mV

–2.5mV

0.01% 10V STEP

POS SLOPE

Figure 42. Instrumentation Amplifier Settling Time to

0.01% for a 10 V Step Input (Positive Slope)

ERROR

TO

SCOPE

TO

INPUT

TO

IN-AMP

OUTPUT

2k

2k

AD9617

549

1k

61.9

+

+

–

–

Figure 43. Settling Time Measurement Circuit

2 MHz BIQUAD BANDPASS FILTER

The circuit in Figure 44 is commonly used in medical imaging

ultrasound receivers. The 30 MHz bandwidth is sufficient to

accurately produce the 2 MHz center frequency, as the mea-

sured response shows in Figure 45. When the op amp’s band-

width is too close to the filter’s center frequency, the amplifier’s

internal phase shift causes excess phase shift at 2 MHz, which

alters the filter’s response. In fact, if the chosen op amp has a

bandwidth close to 2 MHz, the combined phase shift of the

three op amps will cause the loop to oscillate.

Careful consideration must be given to the layout of this circuit

as with any other high speed circuit.

If the phase shift introduced by the layout is large enough, it

could alter the circuit performance, or worse, it will oscillate.

2k

R1

3k

R3

2k

R2

2k

R4

2k

R5

2k

C2

50pF

C1

50pF

R6

1k

+

–

+

–

+

–

+

–

1/4

OP467

1/4

OP467

1/4

OP467

1/4

OP467

Figure 44. 2 MHz Biquad Filter

–20

100k

100M

10M

1M

10k

–10

0

–40

–30

FREQUENCY – Hz

Figure 45. Biquad Filter Response