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### AD603程控增益调整功能的芯片详解 #### 概述 AD603是一种具有程控增益调整功能的芯片，由美国ADI公司研发并持有专利。该芯片是一款低噪声、高带宽（最高90MHz）且增益可调的集成运放。AD603的特点在于其增益控制是线性的，并且是以分贝为单位的，这意味着可以通过控制电压来精确调节其增益值。 #### 特点 1. **线性分贝增益控制**：AD603的增益控制是线性的，增益与控制电压之间存在精确的线性关系，使得用户能够轻松地通过改变控制电压来调整增益大小。 2. **可编程增益范围**：该芯片支持多种预设的增益范围，例如-11dB到+31dB时带宽为90MHz，或者9dB到51dB时带宽缩小至9MHz。此外，还可以通过一个外部电阻器实现任何中间增益范围的设置，比如-1dB到+41dB时，带宽保持在30MHz。 3. **带宽独立于可变增益**：即使在调整增益的情况下，AD603的带宽也保持相对稳定，不会随着增益的变化而变化。 4. **低输入噪声**：输入端的噪声密度仅为1.3nV/√Hz，这在高频放大器中是一个非常优秀的性能指标。 5. **典型增益精度**：通常情况下，增益的准确度可以达到±0.5dB，这对于许多应用场景来说已经足够精确。 6. **高阻抗控制输入**：控制电压输入端口的阻抗高达50MΩ，偏置电流仅为200nA，这些特性使得控制更加灵活方便。 #### 应用领域 - **射频/中频自动增益控制（RF/IF AGC）放大器**：适用于无线通信系统中的射频或中频信号处理。 - **视频增益控制**：在视频信号处理中用于动态调整视频信号的强度，以适应不同的显示需求。 - **模数转换范围扩展（A/D Range Extensions）**：提高模数转换器对输入信号的适应能力，尤其是在信号幅度变化较大的情况下。 - **信号测量**：在实验室测试和信号分析中提供稳定的信号增益调整能力。 #### 总体描述 AD603是一款专为射频和中频自动增益控制系统设计的低噪声电压控制型放大器。它提供了准确且可通过引脚选择的增益范围，如-11dB到+31dB时带宽可达90MHz，或者9dB到51dB时带宽降低至9MHz。用户还可以利用一个外部电阻来设置任何中间增益范围，例如-1dB到+41dB时带宽保持在30MHz。输入端的噪声密度仅为1.3nV/√Hz，推荐的±5V电源供电下功耗为125mW。线性分贝增益经过精确校准，并且在整个温度范围内以及不同电源条件下都保持稳定。增益控制通过高阻抗（50MΩ）、低偏置（200nA）的差分输入进行；增益控制的斜率为25mV/dB，仅需1V的控制电压即可覆盖中间40dB的增益范围。无论选择何种增益范围，均提供1dB的过量和欠量增益。增益控制响应时间对于40dB的变化小于1μs。差分增益控制接口支持差分或单端正负控制电压的应用。多个这样的放大器可以级联，并且可以通过调整它们的增益控制增益来优化系统的信噪比。 AD603能够驱动低至100Ω的负载，并且失真很低。对于500Ω的负载，... #### 结论 AD603是一款高性能的程控增益调整芯片，不仅具有低噪声、高带宽的特点，还拥有出色的增益控制精度和灵活性。无论是应用于射频/中频自动增益控制放大器还是视频信号处理等领域，都能发挥重要作用，为各种电子设备提供可靠的信号处理解决方案。

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Low Noise, 90 MHz

Variable Gain Amplifier

AD603

Rev. I

Information furnished by Analog Devices is believed to be accurate and reliable. However, no

responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other

rights of third parties that may result from its use. Specifications subject to change without notice. No

license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

Trademarks and registered trademarks are the property of their respective owners.

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781.329.4700 www.analog.com

FEATURES

Linear-in-dB gain control

Pin-programmable gain ranges

−11 dB to +31 dB with 90 MHz bandwidth

9 dB to 51 dB with 9 MHz bandwidth

Any intermediate range, for example −1 dB to +41 dB

with 30 MHz bandwidth

Bandwidth independent of variable gain

1.3 nV/√Hz input noise spectral density

±0.5 dB typical gain accuracy

APPLICATIONS

RF/IF AGC amplifiers

Video gain controls

A/D range extensions

Signal measurements

GENERAL DESCRIPTION

The AD603 is a low noise, voltage-controlled amplifier for use

in RF and IF AGC systems. It provides accurate, pin-selectable

gains of −11 dB to +31 dB with a bandwidth of 90 MHz or +9 dB to

51+ dB with a bandwidth of 9 MHz. Any intermediate gain

range may be arranged using one external resistor. The input

referred noise spectral density is only 1.3 nV/√Hz, and power

consumption is 125 mW at the recommended ±5 V supplies.

The decibel gain is linear in dB, accurately calibrated, and stable

over temperature and supply. The gain is controlled at a high

impedance (50 MΩ), low bias (200 nA) differential input; the

scaling is 25 mV/dB, requiring a gain control voltage of only

1 V to span the central 40 dB of the gain range. An overrange

and underrange of 1 dB is provided whatever the selected range.

The gain control response time is less than 1 μs for a 40 dB change.

The differential gain control interface allows the use of either

differential or single-ended positive or negative control voltages.

Several of these amplifiers may be cascaded and their gain

control gains offset to optimize the system SNR.

The AD603 can drive a load impedance as low as 100 Ω with

low distortion. For a 500 Ω load in shunt with 5 pF, the total

harmonic distortion for a ±1 V sinusoidal output at 10 MHz is

typically −60 dBc. The peak specified output is ±2.5 V minimum

into a 500 Ω load.

The AD603 uses a patented proprietary circuit topology—the

X-AMP®. The X-AMP comprises a variable attenuator of 0 dB

to −42.14 dB followed by a fixed-gain amplifier. Because of the

attenuator, the amplifier never has to cope with large inputs and

can use negative feedback to define its (fixed) gain and dynamic

performance. The attenuator has an input resistance of 100 Ω,

laser trimmed to ±3%, and comprises a 7-stage R-2R ladder

network, resulting in an attenuation between tap points of

6.021 dB. A proprietary interpolation technique provides a

continuous gain control function that is linear in dB.

The AD603 is specified for operation from −40°C to +85°C.

FUNCTIONAL BLOCK DIAGRAM

SCALING

REFERENCE

GAIN-

CONTROL

INTERFACE

AD603

PRECISION PASSIVE

INPUT ATTENUATOR

FIXED-GAIN

AMPLIFIER

*NOMINAL VALUES.

R-2R LADDER NETWORK

VPOS

VNEG

GPOS

GNEG

VINP

COMM

0dB –6.02dB –12.04dB –18.06dB –24.08dB –30.1dB –36.12dB –42.14dB

RR R R R R R

2R 2R 2R 2R 2R 2R R

20Ω*

694Ω*

6.44kΩ*

VOUT

FDBK

00539-001

Figure 1.

AD603

Rev. I | Page 2 of 24

TABLE OF CONTENTS

Features .............................................................................................. 1

Applications ....................................................................................... 1

General Description ......................................................................... 1

Functional Block Diagram .............................................................. 1

Revision History ............................................................................... 2

Specifications ..................................................................................... 3

Absolute Maximum Ratings ............................................................ 4

ESD Caution .................................................................................. 4

Pin Configurations and Function Descriptions ........................... 5

Typical Performance Characteristics ............................................. 6

Theory of Operation ...................................................................... 11

Noise Performance ..................................................................... 11

The Gain Control Interface ....................................................... 12

Programming the Fixed-Gain Amplifier Using Pin Strapping

....................................................................................................... 12



Using the AD603 in Cascade ........................................................ 14

Sequential Mode (Optimal SNR) ............................................. 14

Parallel Mode (Simplest Gain Control Interface) .................. 16

Low Gain Ripple Mode (Minimum Gain Error) ................... 16

Applications Information .............................................................. 17

A Low Noise AGC Amplifier .................................................... 17

Caution ........................................................................................ 18

Evaluation Board ............................................................................ 19

Outline Dimensions ....................................................................... 21

Ordering Guide .......................................................................... 21

REVISION HISTORY

3/10—Rev. H to Rev. I

Added Figure 48; Renumbered Sequentially ............................. 19

Added Figure 52 and Figure 53..................................................... 20

Deleted Table 5; Renumbered Sequentially ................................ 20

5/07—Rev. G to Rev. H

Changes to Layout .......................................................................... 14

Changes to Layout .......................................................................... 15

Changes to Layout .......................................................................... 16

Inserted Evaluation Board Section, and Figure 48 to

Figure 51 .......................................................................................... 19

Inserted Figure 52 and Table 4 ...................................................... 20

Changes to Ordering Guide .......................................................... 21

3/05—Rev. F to Rev. G

Updated Format .................................................................. Universal

Change to Features ........................................................................... 1

Changes to General Description .................................................... 1

Change to Figure 1 ........................................................................... 1

Changes to Specifications ................................................................ 3

New Figure 4 and Renumbering Subsequent Figures.................. 6

Change to Figure 10 ......................................................................... 7

Change to Figure 23 ......................................................................... 9

Change to Figure 29 ....................................................................... 12

Updated Outline Dimensions ....................................................... 20

4/04—Rev. E to Rev. F

Changes to Specifications ................................................................. 2

Changes to Ordering Guide ............................................................. 3

8/03—Rev. D to Rev E

Updated Format .................................................................. Universal

Changes to Specifications ................................................................. 2

Changes to TPCs 2, 3, 4 .................................................................... 4

Changes to Sequential Mode (Optimal S/N Ratio) section ......... 9

Change to Figure 8 ......................................................................... 10

Updated Outline Dimensions ....................................................... 14

AD603

Rev. I | Page 3 of 24

SPECIFICATIONS

@ T

= 25°C, V

= ±5 V, –500 mV ≤ V

≤ +500 mV, GNEG = 0 V, –10 dB to +30 dB gain range, R

= 500 Ω, and C

= 5 pF, unless

otherwise noted.

Table 1.

Parameter Conditions Min Typ Max Unit

INPUT CHARACTERISTICS

Input Resistance Pin 3 to Pin 4 97 100 103 Ω

Input Capacitance 2 pF

Input Noise Spectral Density

Input short-circuited 1.3 nV/√Hz

Noise Figure f = 10 MHz, gain = maximum, R

= 10 Ω 8.8 dB

1 dB Compression Point f = 10 MHz, gain = maximum, R

= 10 Ω −11 dBm

Peak Input Voltage ±1.4 ±2 V

OUTPUT CHARACTERISTICS

−3 dB Bandwidth V

OUT

= 100 mV rms 90 MHz

Slew Rate R

≥ 500 Ω 275 V/μs

Peak Output

≥ 500 Ω ±2.5 ±3.0 V

Output Impedance f ≤ 10 MHz 2 Ω

Output Short-Circuit Current 50 mA

Group Delay Change vs. Gain f = 3 MHz; full gain range ±2 ns

Group Delay Change vs. Frequency V

= 0 V; f = 1 MHz to 10 MHz ±2 ns

Differential Gain 0.2 %

Differential Phase 0.2 Degree

Total Harmonic Distortion f = 10 MHz, V

OUT

= 1 V rms −60 dBc

Third-Order Intercept f = 40 MHz, gain = maximum, R

= 50 Ω 15 dBm

ACCURACY

Gain Accuracy, f = 100 kHz; Gain (dB) = (40 V

+ 10) dB −500 mV ≤ V

≤ +500 mV −1 ±0.5 +1 dB

MIN

to T

MAX

−1.5 +1.5 dB

Gain, f = 10.7 MHz V

= -0.5 V −10.3 −9.0 −8.0 dB

= 0.0 V +9.5 +10.5 +11.5 dB

= 0.5 V +29.3 +30.3 +31.3 dB

Output Offset Voltage

= 0 V −20 +20 mV

MIN

to T

MAX

−30 +30 mV

Output Offset Variation vs. V

−500 mV ≤ V

≤ +500 mV −20 +20 mV

MIN

to T

MAX

−30 +30 mV

GAIN CONTROL INTERFACE

Gain Scaling Factor 100 kHz 39.4 40 40.6 dB/V

MIN

to T

MAX

38 42 dB/V

10.7 MHz 38.7 39.3 39.9 dB/V

GNEG, GPOS Voltage Range

−1.2 +2.0 V

Input Bias Current 200 nA

Input Offset Current 10 nA

Differential Input Resistance Pin 1 to Pin 2 50 MΩ

Response Rate Full 40 dB gain change 80 dB/μs

POWER SUPPLY

Specified Operating Range ±4.75 ±6.3 V

Quiescent Current 12.5 17 mA

MIN

to T

MAX

20 mA

Typical open or short-circuited input; noise is lower when system is set to maximum gain and input is short-circuited. This figure includes the effects of both voltage

and current noise sources.

Using resistive loads of 500 Ω or greater or with the addition of a 1 kΩ pull-down resistor when driving lower loads.

The dc gain of the main amplifier in the AD603 is ×35.7; therefore, an input offset of 100 μV becomes a 3.57 mV output offset.

GNEG and GPOS, gain control, and voltage range are guaranteed to be within the range of −V

+ 4.2 V to +V

− 3.4 V over the full temperature range of −40°C to +85°C.