OP467

Rev. | Page 15 of 20

2 MHz BIQUAD BAND-PASS FILTER

0.01% 10V STEP

VS = ±15V

NEG SLOPE

The circuit in Figure 48 is commonly used in medical imaging

ultrasound receivers. The 30 MHz bandwidth is sufficient to

accurately produce the 2 MHz center frequency, as the measured

response shows in Figure 49. When the bandwidth of the op

amp is too close to the center frequency of the filter, the internal

phase shift of the amplifier causes excess phase shift at 2 MHz,

which alters the response of the filter. In fact, if the chosen op

amp has a bandwidth close to 2 MHz, the combined phase shift

of the three op amps causes the loop to oscillate.

2.5mV

–2.5mV

Careful consideration must be given to the layout of this circuit

as with any other high speed circuit.

Figure 45. Instrumentation Amplifier Settling Time to 0.01% for a

10 V Step Input (Negative Slope)

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

alter the circuit performance, or worse, cause oscillation.

0.01% 10V STEP

VS =±15V

POS SLOPE

2.5mV

–2.5mV

VIN

VOUT

1/4

OP467

1/4

OP467

1/4

OP467

1/4

OP467

R1

3kΩ

2kΩ

R2

2kΩ

R6

1kΩ

C1

50pF

C2

50pF

R3

2kΩ

R4

2kΩ

R5

2kΩ

Figure 46. Instrumentation Amplifier Settling Time to 0.01% for a

10 V Step Input (Positive Slope)

Figure 48. 2 MHz Biquad Filter

+VS

AD9617

FREQUENCY (Hz)

–30

–20

–10

0

10k

100k

1M

10M

100M

–40

+

+

–VS

2kΩ

1kΩ

TO

INPUT

TO

IN-AMP

OUTPUT

ERROR

TO SCOPE

2kΩ

61.9Ω

549Ω

Figure 47. Settling Time Measurement Circuit

Figure 49. Biquad Filter Response