A 0.55-V Oscillator with Improved Stability Against Temperature and Supply-Voltage Variations

A compact nanopower all-MOSFET current reference generator (CRG) with low temperature coefficient (TC) and reduced line sensitivity (LS) is presented. Temperature voltages are derived from PTAT and CTAT cells, V/I-converted through a differential pair with LS enhancement and then added to form the reference current I
REF
. The CRG controls a current-starved ring oscillator (CSRO) made up of delay-stages with improved TC and LS parameters. The design complies with a standard
$0.18 \mu\mathrm{m}$
CMOS and
$-20^{\circ}\mathrm{C}\leq \mathrm{T}\leq 70^{\circ}\mathrm{C}, 0.55\mathrm{V}\leq \mathrm{V}_{\text{DD}}\leq 0.90\mathrm{V}$
intervals. Theoretical analysis is backed up by SPICE data. CRG features
$\mathrm{I}_{\text{REF}}=27\text{nA},\ \text{TC}=\text{15.1}\text{ppm}/^{\circ}\mathrm{C},\text{LS}=1.07\%/\mathrm{V},\ \text{PSR}=-116\text{dB}{@}1\text{MHz}$
and 15nW-consumption, with an estimated area of 0.0017mm
²
. CSRO has nominal frequency
$\mathrm{f}_{\text{OSC}}=1.443\text{MHz},\ \text{TC}=269\text{ppm}/^{\circ}\mathrm{C},\ \text{LS}=0.27\%/\mathrm{V}$
, phase error of 0.117rad and 181nW-dissipation. A simple tunning scheme adjusts f
OSC
within [1.27MHz-1.60MHz] range.