Low Cost, DC - 500 MHz, 92 DB Logarithmic Amplifier
The AD8307 is the first Logarithmic Amplifier made available in an 8-lead (SOIC-8) package. It is a complete 500 MHz monolithic demodulating Logarithmic Amplifier based on the progressive compression (successive detection) technique, providing a dynamic range of 92 dB to 3 dB law-conformance and 88 dB to a tight 1 dB error bound at all frequencies up to 100 MHz. It is extremely stable and easy to use, requiring no significant external components. A single supply voltage of 2.7 V to 5.5 V at 7.5 mA is needed, corresponding to an unprecedented power consumption of only 22.5 mW at 3 V. A fast-acting CMOS-compatible control pin CAN disable the AD8307 to a standby current of less than 150 A.
Each of the cascaded Amplifier limiter cells has a small signal gain of 14.3 dB, with a -3 dB bandwidth of 900 MHz. The input is fully differential and at a moderately high impedance (1.1 k in parallel with about 1.4 pF). The AD8307 provides a basic dynamic range extending from approximately -75 dBm (where dBm refers to a 50 source, that is, a sine amplitude of about 56 V) up to +17 dBm (a sine amplitude of 2.2 V). A simple input matching network CAN lower this range to -88 dBm to +3 dBm. The logarithmic linearity is typically within 0.3 dB up to 100 MHz over the central portion of this range, and degrades only slightly at 500 MHz. There is no minimum frequency limit. The AD8307 CAN be used at Audio frequencies of 20 Hz or lower.
The AD8307 operates over the industrial temperature range of -40C to +85C, and is available in 8-lead SOIC and PDIP packages.
By Analog Devices, Inc.
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