Page 48 - EETimes Europe June 2021

48 EE|Times EUROPE

Wolfspeed’s GaN on SiC Tackles Broadband Design Challenges

which is difficult with broadband.
GaN-based designs typically use
an RC circuit, with the block in the
matching section providing most of
the response shaping. The resistance
(R) in the RC network helps bring
down the gain and stabilize lower
frequencies. Smaller capacitance (C)
values have higher impedances at low
frequencies, thus sending more of the
RF signal through R and lowering gain.
Wolfspeed, however, chose the
T-Equalizer architecture because both
the resistances in the RC blocks as well
as the shunt resistance help stabilize
the response. With some tuning, this
architecture offers significant flexibil-
ity in shaping the response.
Figure 5: Wolfspeed’s CG2H40035F-AMP1 reference board exceeds performance
specifications. THE FINAL EVALUATION BOARD
After final evaluations that included check-
ing the design with a 2-W input across the
addressed to avoid poor gain flatness. The desired response band and doing an EM of the entire circuit to check for unanticipated
shaping can be achieved by tweaking the return loss at low coupling, Wolfspeed achieved a close match between modeled and
and high frequencies, taking care to deal with unwanted measurement results.
reflections. The result of this clever design engineering effort is the
CG2H40035F-AMP1 board (Figure 5), with the performance mostly
3. The DC block method for input matching is not suitable exceeding specification requirements.
for broadband. Watch the webinar on designing the amplifier to learn in more detail
The typical approach for input matching is with a DC block of Wolfspeed’s design tips and tricks (bit.ly/3ykCumG), and download
(Figure 4, top) on the input near the connector. This relies on the information on CG2H40035F and the AMP1 board
the matching circuit itself for the gain shaping and return loss, (www.wolfspeed.com/cg2h40035-493). ■

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JUNE 2021 | www.eetimes.eu