AD8367 Linear-in-dB VGA IC Chip

AD8367(500 MHz, Linear-in-dB VGA with AGC Detector)

Introduction

The AD8367 is a high performance 45 dB variable gain amplifier with linear-in-dB gain control for use from low frequencies up to several hundred megahertz. Analog Devices achieves the range, flatness, and accuracy of the gain response using their X-AMP® architecture, the latest in a series of powerful proprietary concepts for variable gain applications, which surpasses what can be achieved using competing techniques.

The 9-stage, 200Ω resistive ladder network applies the input. Each stage applies 5dB of loss, resulting in a total attenuation of 45 dB. When operating at maximum gain, it selects the first tap. As the gain decreases progressively, the tap smoothly and continuously shifts towards higher attenuation values. Following the attenuator is a 42.5dB fixed gain feedback amplifier, which essentially behaves like an operational amplifier with a gain bandwidth product of 100 GHz. This amplifier maintains linearity, even at high frequencies.The output third order intercept is +20 dBV at 100 MHz (+27 dBm,re 200Ω), measured at an output level ofl Vp-p with Vs=5V.

The analog gain-control input scales at 20 mV/dB and ranges from 50 mV to 950 mV. This range corresponds to a gain of -2.5 dB to +42.5 dB when selecting the gain up mode, and +42.5 dB to -2.5 dB when selecting the gain down mode. It’s necessary to select the gain down, or inverse, mode when operating in AGC. In this mode, an integrated square-law detector with an internal setpoint is used to level the output to 354 mV rms, regardless of the crest factor of the output signal. A single external capacitor establishes the loop averaging time.

The voltage applied to the ENBL pin powers on or off the AD8367. When this voltage is at a logic LO, the total power dissipation drops to the milliwatt range. For a logic HI,the chip powers up rapidly to its normal quiescent current of 26 mA at 25°C. The AD8367 is available in a 14-lead TSSOP package for the industrial temperature range of -40°C to +85°C.

Features

• Broad-range analog variable gain: -2.5 dB to +42.5 dB
• 3 dB cutoff frequency of 500 MHz
• Gain up and gain down modes
• Linear-in-dB, scaled 20 mV/dB
• Resistive ground referenced input
• Nominal Z_IN = 200Ω
• On-chip, square-law detector
• Single-supply operation: 2.7 V to 5.5V

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