I’m designing a low power wakeup receiver (WuRx) circuit that will be used to wake up an Arduino and its 433 MHz transceiver, both of which pull way too much current (tens of milliamps) to keep running at each remote node. The goal is to develop a low power wake up receiver / detector that will wake up Arduino (or any sleeping MCU) when RF wake up signal is present. The RF wake up signal will be a series of brief OOK pulses from the transmitter.
I need to amplify the UHF signal from its ten microvolt antenna level, to at least 100 millivolt to 1 volt level in order to detect the RF envelope via a simple diode rectifier, which will then trip a comparator indicating “RF present” during OOK (on-off keying). These pulses will then be counted using some flip/flops or a counter within a given time window to detect a valid wake up signal.
I have done extensive research on these wake up receivers and prior art. Traditional conversion of RF to IF results in too much quiescent current due to the LO current. This has led me to conclude that a low power RF amp fed by a ceramic bandpass filter can solve this problem.
Since this is simply an RF wake up detector, linearity during amplification is much less important than very low quiescent current when no RF is present. These IoT style slave sensors typically sit idle 99.999% of the time, only needing to awaken for a few tens of milliseconds whenever the master polls them.
The flow will look something like this:
Antenna -> Bandpass Filter -> RF Amp -> OOK Envelope Detector -> Wakeup Interrupt to Arduino -> Transceiver Wakeup -> Rx Data -> Process Rx Data -> Back to Sleep
My problem is how to minimize the quiescent amplifier current drain (to nanoamp level ideally) yet sufficiently amplify the microvolt signal once its present and coming out of the bandpass filter. Total amplifier current drain when RF signal is present can be a few milliamps. I’m thinking several 15 dB to 20 dB amplification stages in series to yield a 10,000 to 100,000 x signal boost should be sufficient; e.g. 10 uV to 100mV - 1V.
I’m looking at LNA transistors like the BFP720, a low noise silicon germanium BJT, but willing to consider all low cost options. Low cost and small footprint are also factors but low quiescent current consumption on 3V battery power is critical.
I’ve tried Class C amplifiers with resonant circuits but simulations are failing (using SystemVision simulator) due to low (millivolt) level input signals being too tiny to allow the transistor to conduct. What type of amplifier can I use that has very low quiesce bias current and can amplify this tiny UHF signal?
If I can figure this out, it will help a lot of folks out who are struggling to solve this type of low power wake up problem.
Thanks in advance for guidance.