AD8362
The evaluation board for the AD8362 includes a 1:4 balun,
part number M/A-COM ETC1.6-4-2-3, providing low loss
coupling from 0.5 GHz to 2.5 GHz and an impedance
transformation from the board’s 50 Ω input (at the SMA
connector) to the 200 Ω differential input resistance of the
AD8362. At high frequencies, the actual impedance at the
connector is influenced by reactive aspects of the IC’s input
impedance. Because these can alter the magnitude of the input
voltage, the logarithmic intercept cannot be precisely specified.
However, the shift is temperature stable.
Note that the balun used here increases the signal voltage by the
square root of its impedance ratio of 4:1, in this case by a factor
of 2. The use of a transformer to match the 500 Ω source to the
200 Ω load presented by the AD8362 thus increases the effective
sensitivity of the measurement system by 6 dB, whether
specified in dBV or dBm at the input to the transformer.
Rev. B | Page 28 of 36
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