Tone-based wake up circuit for card reader

A wake-up circuit for a portable card reader, comprising:

• a conditioning circuit comprising a capacitor coupled to an audio signal, and a bias circuit coupled to an input voltage, whereby the capacitor is configured to block any DC component on the audio signal and whereby the bias circuit is configured to bias the input voltage to a biased input voltage;
• a comparator coupled to the audio signal and the biased input voltage, whereby the comparator is configured to output a wake-up signal whenever the voltage of the audio signal is greater than the voltage of the biased input voltage;
• and
• an envelope detector connected to the output of the comparator, the envelope detector configured to convert the wake-up signal to a DC voltage wake-up signal.

A card reader comprising:

• an audio plug configured to be inserted into an audio jack of a mobile device;
• a slot for receiving a payment card;
• a media reading device for reading information off the payment card;
• a wake up circuit comprising:
• a conditioning circuit comprising a capacitor coupled to an audio input of the audio jack of the mobile device, and a bias circuit coupled to a microphone bias signal, whereby the capacitor is configured to block any DC component on the audio input and whereby the bias circuit is configured to bias the microphone bias signal to a biased input voltage;
• a comparator coupled to the audio input and the biased input voltage, whereby the comparator is configured to output a wake-up signal whenever the voltage of the audio input is greater than the voltage of the biased input voltage;
• and
• an envelope detector connected to the output of the comparator, the envelope detector configured to convert the wake-up signal from the comparator to a DC voltage wake-up signal.