AD8310ARMZ-REEL71 AD [Analog Devices], AD8310ARMZ-REEL71 Datasheet - Page 13

• Manufacturer Part Number: AD8310ARMZ-REEL71
• Description: Fast, Voltage-Out DC-440 MHz, 95 dB Logarithmic Amplifier
• Manufacturer: AD [Analog Devices]

For zero-signal conditions, all the detector output currents are
equal. For a finite input of either polarity, their difference is
converted by the output interface to a single-sided unipolar
current, nominally scaled 2 µA/dB (40 µA/decade), at the
output pin BFIN. An on-chip resistor, R1, of ~3 kΩ converts this
current to a voltage of 6 mV/dB. This is then amplified by a
factor of 4 in the output buffer, which can drive a current of up
to 25 mA in a grounded load resistor. The overall rise time of
the AD8310 is under 15 ns. There is also a delay time of about
6 ns when the log amp is driven by an RF burst, starting at zero
amplitude.
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When driving capacitive loads, it is desirable to add a low value
of load resistor to speed up the return to the baseline; the buffer
is stable for loads of a least 100 pF. The output bandwidth can
be lowered by adding a grounded capacitor at BFIN. The time-
constant of the resulting single-pole filter is formed with the
3 kΩ internal load resistor (with a tolerance of 20%). Therefore,
to set the –3 dB frequency to 20 kHz, use a capacitor of 2.7 nF.
Using 2.7 µF, the filter corner is at 20 Hz.
AD8310