Image AD603
型号: AD603
厂商: Analog Devices Inc Analog Devices Inc
分类: 半导体
描述: low noise, 90 mhz variable-gain amplifier
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Low Noise, 90 MHz  
Variable Gain Amplifier  
AD603  
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.  
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  
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.  
APPLICATIONS  
RF/IF AGC amplifiers  
Video gain controls  
A/D range extensions  
Signal measurements  
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 ±3ꢀ, 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.  
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 AD603 is specified for operation from −40°C to +85°C.  
FUNCTIONAL BLOCK DIAGRAM  
8
6
1
2
VPOS  
VNEG  
GPOS  
GNEG  
SCALING  
REFERENCE  
PRECISION PASSIVE  
INPUT ATTENUATOR  
FIXED-GAIN  
AMPLIFIER  
7
5
VOUT  
FDBK  
V
G
6.44k*  
GAIN-  
AD603  
CONTROL  
INTERFACE  
694*  
20*  
0dB  
–6.02dB –12.04dB –18.06dB –24.08dB –30.1dB –36.12dB –42.14dB  
3
4
VINP  
R
R
R
R
R
R
R
2R  
2R  
2R  
2R  
2R  
2R  
R
COMM  
R-2R LADDER NETWORK  
*NOMINAL VALUES.  
Figure 1.  
Rev. H  
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 registeredtrademarks arethe property of their respective owners.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781.329.4700  
Fax: 781.461.3113  
www.analog.com  
©2007 Analog Devices, Inc. All rights reserved.