Datasheet

ManualsBrandsANALOG DEVICES ManualsLinear ICsLinear IC - Op-amp J-FET SOIC 8

Dual, 16 MHz, Rail-to-Rail

FET Input Amplifier

AD823

Rev. A

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FEATURES

Single-supply operation

Output swings rail-to-rail

Input voltage range extends below ground

Single-supply capability from 3 V to 36 V

High load drive

Capacitive load drive of 500 pF, G = +1

Output current of 15 mA, 0.5 V from supplies

Excellent ac performance on 2.6 mA/amplifier

−3 dB bandwidth of 16 MHz, G = +1

350 ns settling time to 0.01% (2 V step)

Slew rate of 22 V/µs

Good dc performance

800 µV max input offset voltage

2 µV/°C offset voltage drift

25 pA max input bias current

Low distortion: −108 dBc worst harmonic @ 20 kHz

Low noise: 16 nV/√Hz @ 10 kHz

No phase inversion with inputs to the supply rails

APPLICATIONS

Battery-powered precision instrumentation

Photodiode preamps

Active filters

12-bit to 16-bit data acquisition systems

Medical instrumentation

GENERAL DESCRIPTION

The AD823 is a dual precision, 16 MHz, JFET input op amp that

can operate from a single supply of +3.0 V to +36 V or from

dual supplies of ±1.5 V to ±18 V. It has true single-supply capa-

bility with an input voltage range extending below ground in

single-supply mode. Output voltage swing extends to within

50 mV of each rail for I

OUT

≤ 100 µA, providing outstanding

output dynamic range.

An offset voltage of 800 µV maximum, an offset voltage drift of

2 µV/°C, input bias currents below 25 pA, and low input voltage

noise provide dc precision with source impedances up to a

Gigohm. It provides 16 MHz, −3 dB bandwidth, −108 dB THD

@ 20 kHz, and a 22 V/µs slew rate with a low supply current of

2.6 mA per amplifier. The AD823 drives up to 500 pF of direct

capacitive load as a follower and provides an output current of

15 mA, 0.5 V from the supply rails. This allows the amplifier to

handle a wide range of load conditions.

CONNECTION DIAGRAM

AD823

OUT1

+IN2

–IN2

OUT2

–IN1

+IN1

–V

00901-A-001

Figure 1. 8-Lead PDIP and SOIC

GND

= 100kΩ

= 50pF

= 3V

500mV

200µs

00901-A-002

Figure 2. Output Swing, V

= 3 V, G = +1

FREQUENCY (Hz)

–8

OUTPUT (dB)

–6

–7

10k 100k 1M

= 5V

G = +1

–5

–4

–3

–2

–1

10M

00901-A-003

Figure 3. Small Signal Bandwidth, G = +1

This combination of ac and dc performance, plus the

outstanding load drive capability, results in an exceptionally

versatile amplifier for applications such as A/D drivers, high

speed active filters, and other low voltage, high dynamic range

systems.

The AD823 is available over the industrial temperature range of

−40°C to +85°C and is offered in both 8-lead PDIP and SOIC

packages.

Summary of content (20 pages)

PAGE 1
Dual, 16 MHz, Rail-to-Rail FET Input Amplifier AD823 CONNECTION DIAGRAM Single-supply operation Output swings rail-to-rail Input voltage range extends below ground Single-supply capability from 3 V to 36 V High load drive Capacitive load drive of 500 pF, G = +1 Output current of 15 mA, 0.5 V from supplies Excellent ac performance on 2.6 mA/amplifier −3 dB bandwidth of 16 MHz, G = +1 350 ns settling time to 0.
PAGE 2
AD823 TABLE OF CONTENTS Specifications..................................................................................... 3 Absolute Maximum Ratings............................................................ 6 ESD Caution.................................................................................. 6 Typical Performance Characteristics ............................................. 7 Theory of Operation ...................................................................... 13 Output Impedance ........
PAGE 3
AD823 SPECIFICATIONS At TA = 25°C, VS = 5 V, RL = 2 kΩ to 2.5 V, unless otherwise noted. Table 1. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth, VO ≤ 0.2 V p-p Full Power Response Slew Rate Settling Time to 0.1% to 0.
PAGE 4
AD823 At TA = 25°C, VS = 3.3 V, RL = 2 kΩ to 1.65 V, unless otherwise noted. Table 2. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth, VO ≤ 0.2 V p-p Full Power Response Slew Rate Settling Time to 0.1% to 0.
PAGE 5
AD823 At TA = 25°C, VS = ±15 V, RL = 2 kΩ to 0 V, unless otherwise noted. Table 3. Parameter DYNAMIC PERFORMANCE −3 dB Bandwidth, VO ≤ 0.2 V p-p Full Power Response Slew Rate Settling Time to 0.1% to 0.
PAGE 6
AD823 ABSOLUTE MAXIMUM RATINGS Table 4. Rating 36 V 2.0 8-LEAD PDIP Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. 1 1.5 1.0 8-LEAD SOIC 0.
PAGE 7
AD823 TYPICAL PERFORMANCE CHARACTERISTICS 80 100 70 60 VS = 5V 317 UNITS σ = 0.4pA 90 VS = 5V 314 UNITS σ = 40µV 80 70 60 UNITS UNITS 50 40 50 40 30 30 20 20 10 –100 –50 0 50 100 INPUT OFFSET VOLTAGE (µV) 200 150 0 0 2 3 4 5 6 7 INPUT BIAS CURRENT (pA) 8 9 10 Figure 8. Typical Distribution of Input Bias Current Figure 5.
PAGE 8
AD823 110 95 VS = 5V RL = 2kΩ 94 93 OPEN-LOOP GAIN (dB) OPEN-LOOP GAIN (dB) 100 VS = ± 2.5V 90 80 92 91 90 89 88 70 86 –55 Figure 11. Open-Loop Gain vs. Load Resistance 95 125 100 100 RL = 10kΩ 80 80 PHASE 100 OPEN-LOOP GAIN (dB) RL = 1kΩ 10 RL = 100Ω 1 60 60 40 40 GAIN 20 20 RL = 2kΩ CL = 20pF 0.1 –2.5 –2.0 –1.5 –1.0 –0.5 0.5 1.0 0 OUTPUT VOLTAGE (V) 1.5 2.0 2.5 00901-A-012 0 –20 100 1k 0 10k 100k 1M 10M –20 100M FREQUENCY (Hz) Figure 15.
PAGE 9
AD823 5 90 G = +1 CL = 20pF RL = 2kΩ CLOSED-LOOP GAIN (dB) 4 3 VS = ±15V 80 VS = +5V 70 2 CMRR (dB) 1 0 +27°C –1 –55°C 60 50 +125°C –2 40 –3 30 –5 0.30 3.27 6.24 9.21 12.18 15.15 18.12 21.09 24.06 27.03 30.00 FREQUENCY (MHz) 20 10 10k 100k FREQUENCY (Hz) 1M 10M 10 VS = 5V 10 1.0 0.01 100 1k 10k 100k FREQUENCY (Hz) 1M 00901-A-018 0.1 10M 1 VS – VOH +25°C 0.1 VOL +25°C VOL +25°C 0.01 0.1 Figure 18. Output Resistance vs.
PAGE 10
AD823 21 90 80 70 +PSRR 60 50 40 –PSRR 30 CL 15 VS = 5V 12 9 φM = 45° 6 φM = 20° 20 10k 100k FREQUENCY (Hz) 1M 10M 00901-A-023 1k 0 0 Figure 23. Power Supply Rejection vs. Frequency 2 3 4 5 6 7 CAPACITOR (pF × 1000) 8 9 10 Figure 26. Capacitive Load vs. Series Resistance 30 –30 RL = 2kΩ G = +1 –40 VS = 5V –50 CROSSTALK (dB) 20 VS = ±15V 10 –60 –70 –80 –90 –100 VS = +5V –110 –130 1k 10k 100k FREQUENCY (Hz) VS = 3V VIN = 2.
PAGE 11
AD823 5V RL = 300Ω CL = 50pF RF = RG = 2kΩ 20µs 5V Figure 29. Output Swing, VS =5 V, G = −1 +15V 20kHz, 20V p-p –15V 50pF 604Ω 00901-A-032 200µs 00901-A-029 500mV GND VS = ±15V VIN = 20V p-p G = +1 Figure 32. Output Swing, VS = ±15 V, G = +1 5V RL = 2kΩ CL = 50pF VS = 3V VIN = 100mV STEP G =+1 1.55V 50ns 500mV 00901-A-033 25mV 00901-A-030 1.45V 100ns GND Figure 30. Pulse Response, VS = 3 V, G = +1 Figure 33.
PAGE 12
AD823 RL = 100kΩ CL = 50pF +10V 5V 500ns 00901-A-035 –10V Figure 35. Pulse Response, VS = ±15 V, G = +1 Rev.
PAGE 13
AD823 THEORY OF OPERATION The AD823 is fabricated on the Analog Devices proprietary complementary bipolar (CB) process that enables the construction of PNP and NPN transistors with similar fTs in the 600 MHz to 800 MHz region. In addition, the process also features N-Channel JFETs, which are used in the input stage of the AD823. These process features allow the construction of high frequency, low distortion op amps with pico-ampere input currents.
PAGE 14
AD823 OUTPUT IMPEDANCE Rev. A | Page 14 of 20 S1N gmVI C1 R1 VOUT S1P C2 gmVI R1 C5 gm2 R2 00901-A-037 The low frequency open-loop output impedance of the common-emitter output stage used in this design is approximately 30 kΩ. While this is significantly higher than a typical emitter follower output stage, when it is connected with feedback, the output impedance is reduced by the open-loop gain of the op amp. With 109 dB of open-loop gain, the output impedance is reduced to <0.2 Ω.
PAGE 15
AD823 APPLICATIONS INPUT CHARACTERISTICS In the AD823, N-Channel JFETs are used to provide a low offset, low noise, high impedance input stage. Minimum input common-mode voltage extends from 0.2 V below −VS to 1 V < +VS. Driving the input voltage closer to the positive rail will cause a loss of amplifier bandwidth and increased commonmode voltage error. The AD823 does not exhibit phase reversal for input voltages up to and including +VS.
PAGE 16
AD823 +5VA 2 10µF 1 VIN 49.9Ω AD823 5 VREF (1.25V) 7 6 4 1kΩ 2 4 9 6 5 7 3 8 +5VD Figure 41. FFT of AD1672 Output Driven by AD823 10µF 8 3 VIN = 2.15V p-p G = +1 FI = 490kHz 1kΩ CLOCK 0.1µF 0.1µF 28 19 +VCC +VDD 20 REFOUT 21 AIN1 15 22 AIN2 13 14 AD1672 12 11 10 9 23 REFIN 8 24 REFCOM 25 NCOMP2 7 26 NCOMP1 6 5 4 3 27 2 ACOM 1 16 10µF 0.1µF The AD823 exhibits good current drive and THD+N performance, even at 3 V single supplies.
PAGE 17
AD823 Second-Order Low-Pass Filter Single-Supply Half-Wave and Full-Wave Rectifiers Figure 43 depicts the AD823 configured as a second-order Butterworth low-pass filter. With the values as shown, the corner frequency will be 200 kHz. The equations for component selection are shown below. An AD823 configured as a unity-gain follower and operated with a single supply can be used as a simple half-wave rectifier.
PAGE 18
AD823 OUTLINE DIMENSIONS 0.375 (9.53) 0.365 (9.27) 0.355 (9.02) 8 5 1 4 0.295 (7.49) 0.285 (7.24) 0.275 (6.98) 0.325 (8.26) 0.310 (7.87) 0.300 (7.62) 0.100 (2.54) BSC 0.015 (0.38) MIN 0.180 (4.57) MAX 0.150 (3.81) 0.130 (3.30) 0.110 (2.79) 0.022 (0.56) 0.018 (0.46) 0.014 (0.36) 0.150 (3.81) 0.135 (3.43) 0.120 (3.05) 0.015 (0.38) 0.010 (0.25) 0.008 (0.20) SEATING PLANE 0.060 (1.52) 0.050 (1.27) 0.045 (1.
PAGE 19
AD823 NOTES Rev.