Low power 433 MHz Wakeup Receiver Amplifier

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Joined Jan 26, 2017
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. The goal is to develop a low power wake up receiver / detector that will wake up Arduino (or any sleeping MCU) when the RF wake up signal is present. The RF wake up signal will be a sequence of OOK pulses from the transmitter.

I need to amplify the UHF signal from its ten microvolt antenna level, to around 500 millivolt level in order to detect the RF envelope via a 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, then interrupt the MCU to wake it.

I have researched wake up receivers and prior art. Traditional conversion of RF to IF results in too much quiescent current due to the LO current. Super regenerative receivers also drain a lot of current. This has led me to hypothesize that a low power RF amp fed by a ceramic bandpass filter can solve this problem, provided the signal can be amplified at low enough power levels and quiescent current is negligible.

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 to hundreds of milliseconds whenever the master polls them.

The flow will look something like this:

Antenna -> Bandpass Filter -> RF Amp -> OOK Envelope Detector -> Wakeup Signal Detector -> Wakeup Interrupt to Arduino -> Transceiver Wakeup -> Rx Data -> Process Rx Data -> Back to Sleep

The challenge is how best 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 5 to 10 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 considering LNA UHF 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.

What type of amplifier has very low quiesce bias current and can amplify this microvolt level UHF signal, even with significant distortion?