The AD8041 is fabricated on Analog Devices’ proprietary
eXtra-Fast Complementary Bipolar (XFCB) process, which
enables the construction of PNP and NPN transistors with similar
fT in the 2 GHz to 4 GHz region. The process is dielectrically
isolated to eliminate the parasitic and latch-up problems caused
by junction isolation. These features allow the construction of
high frequency, low distortion amplifiers with low supply currents.
This design uses a differential output input stage to maximize
bandwidth and headroom (see Figure 5). The smaller signal
swings required on the first stage outputs (nodes S1P, S1N) reduce
the effect of nonlinear currents due to junction capacitances and
improve the distortion performance. With this design harmonic
distortion of better than –85 dB @ 1 MHz into 100 Ω with VOUT =
2 V p-p (Gain = +2) on a single 5 V supply is achieved.