AD8307AR

GENERAL DESCRIPTION

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 μA.
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 kΩ 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 Ω source, that is, a sine amplitude of about ±56 μV) 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 output is a voltage scaled 25 mV/dB, generated by a current of nominally 2 μA/dB through an internal 12.5 kΩ resistor. This voltage varies from 0.25 V at an input of −74 dBm (that is, the ac intercept is at −84 dBm, a 20 μV rms sine input), up to 2.5 V for an input of +16 dBm. This slope and intercept can be trimmed using external adjustments. Using a 2.7 V supply, the output scaling can be lowered, for example to 15 mV/dB, to permit utilization of the full dynamic range.
The AD8307 exhibits excellent supply insensitivity and temperature stability of the scaling parameters. The unique combination of low cost, small size, low power consumption, high accuracy and stability, very high dynamic range, and a frequency range encompassing audio through IF to UHF makes this product useful in numerous applications requiring the reduction of a signal to its decibel equivalent.
The AD8307 operates over the industrial temperature range of −40°C to +85°C, and is available in 8-lead SOIC and PDIP packages.

FEATURES

Complete multistage logarithmic amplifier
92 dB dynamic range: –75 dBm to +17 dBm
to –90 dBm using matching network
Single supply of 2.7 V minimum at 7.5 mA typ
DC to 500 MHz operation, ±1 dB linearity
Slope of 25 mV/dB, intercept of −84 dBm
Highly stable scaling over temperature
Fully differential dc-coupled signal path
100 ns power-up time, 150 μA sleep current

APPLICATIONS
Conversion of signal level to decibel form
Transmitter antenna power measurement
Receiver signal strength indication (RSSI)
Low cost radar and sonar signal processing
Network and spectrum analyzers (to 120 dB)
Signal level determination down to 20 Hz
True decibel ac mode for multimeters