State reduction for efficient digital calibration of analog/RF integrated circuits

Abstract

Calibration of analog/radio-frequency (RF) integrated circuits addresses the problem of yield loss that is a result of the increased variability commonly observed in nanoscale processes. In order to compensate for increased yield loss, calibration techniques have been developed that are applied to fabricated chips, aiming at the restoration of a circuit's performance to its acceptable range of values that are defined by the specifications. To allow calibration, adjustable elements are introduced that provide multiple states of a circuit's operation through built-in tuning knobs. Digital calibration--that refers to the case of discrete tuning knob settings--is performed by switching to a circuit's state at which all performance characteristics are restored to their specified ranges. Due to the large number of performance characteristics of interest a large space of tuning knob settings should be explored, that leads to a series of practical considerations that need to be addressed, such as increased times required for calibration preparation and conduction, or chip area overhead if built-in tuning knobs are used. In this paper we present a method to maintain a desired level of yield recovery through the exploitation of only a minimum number of calibration states, also ensuring low cost by shortening calibration times and reducing chip area overhead. The proposed method is assessed through case studies conducted on a typical RF mixer designed in a 180 nm CMOS technology.