OP270GSZ-REEL2 데이터 시트보기 (PDF) - Analog Devices

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OP270GSZ-REEL2

Dual Very Low Noise Precision Operational Amplifier

Analog Devices 

OP270

LOW PHASE ERROR AMPLIFIER

The simple amplifier depicted in Figure 41 utilizes a monolithic

dual operational amplifier and a few resistors to substantially

reduce phase error compared with conventional amplifier

designs. At a given gain, the frequency range for a specified

phase accuracy is more than a decade greater than that of a

standard single op amp amplifier.

The low phase error amplifier performs second-order fre-

quency compensation through the response of Op Amp A2 in

the feedback loop of A1. Both op amps must be extremely well

matched in frequency response. At low frequencies, the A1

feedback loop forces V2/(K1 + 1) = VIN. The A2 feedback loop

forces VO/(K1 + 1) = V2/(K1 + 1), yielding an overall transfer

function of VO/VIN = K1 + 1. The dc gain is determined by the

resistor divider at the output, VO, and is not directly affected by

the resistor divider around A2. Note that, like a conventional

single op amp amplifier, the dc gain is set by resistor ratios only.

Minimum gain for the low phase error amplifier is 10.

R2 R2 = R1

R2

K2

1/2

OP270E

V2

A2

1/2

OP270E

R1

R1

K1

A1

VIN

ASSUME A1 AND A2 ARE MATCHED.

AO(s)

=

ωT

s

VO

VO = (K1 + 1)VIN

Figure 41. Low Phase Error Amplifier

Figure 42 compares the phase error performance of the low

phase error amplifier with a conventional single op amp

amplifier and a cascaded two-stage amplifier. The low phase

error amplifier shows a much lower phase error, particularly for

frequencies where ω/βωT < 0.1. For example, a phase error of

−0.1° occurs at 0.002 ω/βωT for the single op amp amplifier, but

at 0.11 ω/βωT for the low phase error amplifier.

0

–1

SINGLE OP AMP.

CONVENTIONAL DESIGN

–2

–3

CASCADED

(TWO STAGES)

–4

–5

LOW PHASE ERROR

AMPLIFIER

–6

–7

0.001

0.005 0.01

0.05 0.1

FREQUENCY RATIO (1/βω)(ω/ωT)

Figure 42. Phase Error Comparison

0.5 1

FIVE-BAND, LOW NOISE, STEREO GRAPHIC

EQUALIZER

The graphic equalizer circuit shown in Figure 43 provides 15 dB

of boost or cut over a five-band range. Signal-to-noise ratio over

a 20 kHz bandwidth is better than 100 dB and referred to a 3 V

rms input. Larger inductors can be replaced by active inductors,

but consequently reduces the signal-to-noise ratio.

C1

0.47µF

VIN

R1

47kΩ

1/2

OP270E

R2

3.3kΩ

R3

680Ω

C2

6.8µF

+

L1

TANTALUM 1H

R5

680Ω

C3

1µF

+

TANTALUM

L2

600mH

R7

680Ω

C4

0.22µF

+

L3

180mH

R9

680Ω

C5

0.047µF

+

L4

60mH

R11

680Ω

C6

0.022µF

+

L5

10mH

R4

1kΩ

60Hz

R6

1kΩ

200Hz

R8

1kΩ

800Hz

R10

1kΩ

3kHz

R12

1kΩ

10kHz

1/2

OP270E

R13

3.3kΩ

R14

100Ω

VOUT

Figure 43. Five-Band, Low Noise Graphic Equalizer

Rev. E | Page 16 of 20

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