ADA4817-2ACPZ-R2 datasheet(14/25 Pages) AD

14 / 25 page

ADA4817-1/ADA4817-2

Data Sheet

Rev. C | Page 14 of 25

THEORY OF OPERATION

The ADA4817-1/ADA4817-2 are voltage feedback operational

amplifiers that combine new architecture for FET input operational

amplifiers with the eXtra fast complementary bipolar (XFCB)

process from Analog Devices, resulting in an outstanding

combination of speed and low noise. The innovative high speed

FET input stage handles common-mode signals from the negative

supply to within 2.7 V of the positive rail. This stage is combined

with an H-bridge to attain an 870 V/μs slew rate and low distortion,

in addition to 4 nV/√Hz input voltage noise. The amplifier

features a high speed output stage capable of driving heavy loads

sourcing and sinking up to 40 mA of linear current. Supply current

and offset current are laser trimmed for optimum performance.

These specifications make the ADA4817-1/ADA4817-2 a great

choice for high speed instrumentation and high resolution data

acquisition systems. Its low noise, picoamp input current, precision

offset, and high speed make them superb preamps for fast photo-

diode applications.

CLOSED-LOOP FREQUENCY RESPONSE

The ADA4817-1/ADA4817-2 are classic voltage feedback

amplifiers with an open-loop frequency response that can be

approximated as the integrator response shown in Figure 43. Basic

closed-loop frequency response for inverting and noninverting

configurations can be derived from the schematics shown in

Figure 41 and Figure 42.

VOUT

VIN

Figure 41. Noninverting Configuration

VOUT

VIN

Figure 42. Inverting Configuration

NONINVERTING CLOSED-LOOP FREQUENCY

RESPONSE

Solving for the transfer function,







CROSSOVER













(4)

where fCROSSOVER is the frequency where the open-loop gain of

the amplifier equals 0 dB.

At dc,





(5)

Closed-loop −3 dB frequency

CROSSOVER

3dB









(6)

INVERTING CLOSED-LOOP FREQUENCY RESPONSE

Solving for the transfer function,



CROSSOVER















(7)

At dc





(8)

Solve for closed-loop −3 dB frequency by,

CROSSOVER







3

(9)

FREQUENCY (MHz)

0.1

1000

100

fCROSSOVER = 410MHz

A = (2π ×

fCROSSOVER)/s

Figure 43. Open-Loop Gain vs. Frequency and Basic Connections

The closed-loop bandwidth is inversely proportional to the noise

gain of the op amp circuit, (RF + RG)/RG. This simple model is

accurate for noise gains above 2. The actual bandwidth of circuits

with noise gains at or below 2 is higher than those predicted

with this model due to the influence of other poles in the

frequency response of the real op amp.

Figure 44 shows the dc errors of the voltage feedback amplifier.

For both inverting and noninverting configurations,











































OUT

error

(10)

Ib–

Ib+

+VOS –

VOUT

VIN

Figure 44. DC Errors of the Voltage Feedback Amplifier

ADA4817-2ACPZ-R2 数据表(PDF) 14 Page - Analog Devices

ADA4817-2ACPZ-R2 数据表(HTML) 14 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

数据表下载

链接网址

ADA4817-2ACPZ-R2 数据表(PDF) 14 Page - Analog Devices

ADA4817-2ACPZ-R2 数据表(HTML) 14 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

数据表 下载

链接网址

数据表下载