A Delta-Sigma Pulse-Width Digitization Technique for Super-Regenerative Receivers

This paper presents a delta-sigma pulse-width digitizer (
$\Delta \Sigma$
-PWD) architecture designed for a super-regenerative receiver (SR-RX) operated at the 400-MHz Medical Implantable Communications Service (MICS) band. The
$\Delta \Sigma$
-PWD employs the operation principle of a
$\Delta \Sigma$
modulator to convert the pulse-width (PW) value into digital domain and achieve fine resolution, which allows the SR-RX to support the 2-ASK/4-ASK modulations. It can be considered as the PW domain counterpart of a conventional
$\Delta \Sigma$
modulator. The proposed architecture is capable of suppressing the PW quantization error over the direct-sampling-type PW detector by 23 dB. A linear model for the
$\Delta \Sigma$
-PWD is devised in this paper for system analysis and design optimization. Fabricated in a 0.18-
$\mu{\hbox {m}}$
CMOS process, the whole receiver draws 700
$\mu{\hbox {A}}$
from a 1.3-V supply, while the
$\Delta \Sigma$
-PWD consumes only 100
$\mu{\hbox {A}}$
. When operated on the 4-ASK modulation signal with 312-kbps data rate, the receiver achieves an energy efficiency of 2.9
$~$
nJ/bit and
${-}\hbox{76-dBm}$
sensitivity.