A feedback interference cancellation circuit is presented that uses a control loop to reject blockers in wireless receivers. The concept is based on a feedback translational loop which subtracts a blocker replica from the original blocker signal. In contrast to feedforward methods loop selectivity does not depend on exact gain matching of two paths but on the open loop gain which is easier to adjust. The concept is described including the theoretical derivations of the transfer function and stability. Nonidealities like I/Q mismatch and noise mechanisms are discussed. Finally, measurements from a prototype chip in 65-nm CMOS are presented showing the feasibility of active feedback cancellation. In a desensitization scenario, gain drops by more than 12 dB for a 15 dBm blocker at 20 MHz offset without feedback interference cancellation while a gain degradation of merely 3 dB is measured with feedback interference cancellation enabled.

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Future universal quantum computers solving problems of practical relevance are expected to require at least 10 6 qubits, which is a massive scale-up from the present numbers of less than 50 qubits operated together. Out of the different types of qubits, solid state qubits are considered to be viable candidates for this scale-up, but interfacing to and controlling such a large number of qubits is a complex challenge that has not been solved yet. One possibility to address this challenge is to use qubit control circuits located close to the qubits at cryogenic temperatures. In this work we evaluate the feasibility of this idea, taking as a reference the physical requirements of a two-electron spin qubit and the specifications of a standard 65 nm complementary metal-oxide-semiconductor (CMOS) process. Using principles and flows from electrical systems engineering we provide realistic estimates of the footprint and of the power consumption of a complete control-circuit architecture. Our results show that with further research it is possible to provide scalable electrical control in the vicinity of the qubit, with our concept.

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