AD603 Adjustable Gain amplifier DA input Programmable AGC Module

Description

AD603 Adjustable Gain amplifier DA input Programmable AGC Module
Description
A, AD603 chip introduction
The AD603 is a low noise, voltage controlled amplifier for radio frequency (RF) and intermediate frequency (IF) automatic gain control (AGC) systems. It provides accurate pin selectable gains from −11 dB to +31 dB at 90 MHz bandwidth and +9 dB to +51 dB at 9 MHz bandwidth. Use an external resistor to obtain any intermediate gain range. The input referred noise spectral density is only 1.3 nV/√Hz, and the power consumption is 125 mW with the recommended ±5 V power supply.
The gain is linear in dB and is precisely calibrated and does not change with temperature and supply voltage. The gain is controlled by a high-impedance (50 MΩ), low-bias (200 nA) differential input; the scaling factor is 25 mV/dB, so only 1 V of gain control voltage is needed to cover the mid-range of 40 dB of the gain range. Regardless of the range chosen, 1 dB over-range and under-range are available. For a 40 dB change, the gain control response time is less than 1 μs. The differential gain control interface allows differential or single-ended positive or single-ended negative control voltages. Several such amplifiers can be cascaded with their gain control gain bias to optimize the system signal-to-noise ratio (SNR).
The AD603 can drive load impedances as low as 100 Ω with low distortion. For a 500-Ω load with a 5 pF shunt, the total harmonic distortion of a ±1 V sine output is typically −60 dBc at 10 MHz. The peak rated output into a 500 Ω load is ±2.5 V (minimum).
The AD603 uses a proprietary, patented circuit structure, X-AMP®. The X-AMP contains a 0 dB to -42.14 dB variable attenuator followed by a fixed gain amplifier. Due to the presence of an attenuator, the amplifier never has to process a large input, and negative feedback can be used to define its (fixed) gain and dynamic performance. The attenuator has a 100 Ω input resistor that is laser trimmed to ±3% and contains a 7-stage R-2R ladder network, which provides a 6.021 dB attenuation between contacts. Using proprietary interpolation techniques, linear continuous gain control in dB is available.
The AD603 has an operating temperature range of −40°C to +85°C.
The AGC circuit of the receiver in the shortwave digital communication system is realized by using the AD603 variable gain amplifier combined with a simple AGC control circuit, having a high gain, a dynamic range of 70dB, a bandwidth of 90MHz, and a very simple circuit structure.
When the short-wave receiver receives the signal, the signal level at the input end varies over a large range because of variations in the ionosphere, fading, and conditions of the received signal. The output power of the receiver varies with the size of the external signal, and the signal strength at the output of the receiver will vary greatly. For this reason, automatic gain control (AGC) circuits are very much emphasized in short wave receivers. The AGC circuit is an automatic control circuit that maintains the amplitude of the output signal constant or changes only within a small range in the case where the amplitude of the input signal varies greatly. The basic principle of AGC is to generate a DC AGC voltage that varies with the input level. The AGC voltage is used to control the gain of certain amplifying parts (such as a mid-range), so that the total gain of the receiver changes according to a certain rule. The AGC circuit is mainly composed of a control circuit and a controlled circuit. The control circuit is the generating part of the AGC DC voltage. The function of the controlled circuit is to change the gain of the receiver according to the changed control voltage generated by the control circuit.
At present, there are mainly two methods for controlling the amplifier gain in a shortwave receiver. One is to change the parameters of the amplifier itself to change the gain. Typically, a double-gate FET is used. The gain is changed by changing the dc bias voltage of one of the gates; the other is to insert the amplifier between the amplifier stages. The variable attenuator controls the attenuation and changes the gain. Typically, various variable gain amplifiers are integrated. The AGC circuit discussed in this paper is implemented using Analog Devices' AD603 variable gain amplifier combined with a simple AGC control circuit. The required gain is greater than 50dB, the AGC dynamic range is greater than 65dB, and the output signal level is basically stable at 10dBm.
package ：
1pc
AD603 Adjustable Gain amplifier DA input Programmable AGC Module
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