Methodology for the Digital Calibration of Analog Circuits and
Systems shows how to relax the extreme design constraints in analog
circuits, allowing the realization of high-precision systems even with
low-performance components. A complete methodology is proposed, and
three applications are detailed.
To start with, an in-depth analysis of existing compensation techniques
for analog circuit imperfections is carried out. The M/2+M
sub-binary digital-to-analog converter is thoroughly studied, and the
use of this very low-area circuit in conjunction with a successive
approximations algorithm for digital compensation is described. A
complete methodology based on this compensation circuit and algorithm is
then proposed. The detection and correction of analog circuit
imperfections is studied, and a simulation tool allowing the transparent
simulation of analog circuits with automatic compensation blocks is
introduced.
The first application shows how the sub-binary M/2+M
structure can be employed as a conventional digital-to-analog converter
if two calibration and radix conversion algorithms are implemented.
The second application, a SOI 1T DRAM, is then presented. A digital
algorithm chooses a suitable reference value that compensates several
circuit imperfections together, from the sense amplifier offset to the
dispersion of the memory read currents.
The third application is the calibration of the sensitivity of a current
measurement microsystem based on a Hall magnetic field sensor. Using a
variant of the chopper modulation, the spinning current technique,
combined with a second modulation of a reference signal, the sensitivity
of the complete system is continuously measured without interrupting
normal operation. A thermal drift lower than 50 ppm/°C is achieved,
which is 6 to 10 times less than in state-of-the-art implementations.
Furthermore, the calibration technique also compensates drifts due to
mechanical stresses and ageing.
