In an aspect, a circuit can include a first HEMT, a second HEMT, and a variable capacitor. A drain of the first HEMT can be coupled to a source of the second HEMT. An electrode of the variable capacitor can be coupled to a source of the first HEMT, and another electrode of the variable capacitor can be coupled to a gate of the second HEMT. In another aspect, an electronic device can include a die including a HEMT and a variable capacitor. An electrode of the variable capacitor can be coupled to a source or a gate of the HEMT, and another electrode of the variable capacitor can be coupled to an external terminal of the die. In a further aspect, an electronic device comprising a die, wherein the die includes a variable capacitor, a first diode, and a second diode.