A micropower CMOS, direct-conversion, VLF receiver chip formagnetic-field wireless applications

摘要

A micropower CMOS, direct-conversion very low frequency (VLF)nreceiver is described for receiving low-level magnetic fields fromnresonant sensors. The single-chip, phase locked loop (PLL)-synthesizednreceiver covers a frequency range of 10-82 kHz and provides both analognand 9-b digital baseband I and Q outputs. Digital I and Q outputs arenaccumulated in a companion digital chip which provides baseband signalnprocessing. Emphasis is plated on the receiver micropower RFnpreamplifier which uses a lateral bipolar input device because of thensignificant increase in flicker noise illustrated for PMOS devices innweak inversion. Lateral bipolar transistors are also utilized in thenmixer and IF stages for low flicker noise and low dc offsets. Specialnattention is given to isolating the internal local oscillator signalsnfrom the low-level RF input (0.3 ΜV noise floor in 300 Hz BW), andnlocal oscillator feedthrough is indiscernible in the RF preamplifiernoutput noise spectrum. The 100% duty-cycle receiver, intended fornminiature, battery-operated wireless applications, operatesnapproximately four months at 80 ΜA from a 6-V, 220-mA-hrnbattery