Data Sheet

ADA4961

Rev. C | Page 15 of 24

AC CHARACTERIZATION OUTPUT FILTER

Figure 37 is used in part of the ac characterization of the

ADA4961. The picosecond 5310 balun provides the differential

input signal and the 100 Ω differential match to the device. The

3 dB pads make the picosecond balun 50 Ω impedance less

reactive on one side, which balances the differential phase

accuracy. On the outputs, the 2 nH and 2 pF create a two-pole

low-pass filter, along with the two 50 Ω resistors in parallel with

the pads and output picosecond balun. This filter creates the

50 Ω differential load.

The output pads make the load more balanced. This is essential

for good HD2 performance. This filter technique also creates a

lighter load (slight peaking) for the device at higher frequencies,

which improves the IMD3 performance. Though the filter

bandwidth (BW) computes to 3.3 GHz, the parasitic C (not

shown in Figure 37) across the 2 nH filter inductors reduces the

3 dB BW to about 2 GHz (see Figure 4). The filter, beyond

reducing integrated output noise, also reduces the higher

frequency second and third harmonics above 1 GHz and

700 MHz, respectively (see Figure 20 and Figure 21).