Contactless Interface

Abstract

Power extracted from an antenna inductively coupled to an alternating magnetic field is regulated to provide voltage supplies. In some implementations, a first voltage supply (e.g., 3.8 volts) provides regulated voltage to analog circuits and a second, lower, voltage supply (e.g., 1.4 volts) provides regulated voltage to digital circuits. The first voltage supply is regulated, using shunt regulation, by a first voltage regulator circuit. The second voltage supply is regulated, using a series regulation, by a second voltage regulator circuit. The second voltage regulator circuit is supplied by the shunted current from the first voltage regulator. Excess shunt current provided by the first regulator circuit can be bypassed (e.g., bypassed to ground). The second voltage regulator circuit can use a timer circuit to control the amount of charge transferred to a second voltage supply rail. The timer circuit can compensate for different currents from the first voltage regulator circuit.

1 . A circuit comprising:
 an input configured for coupling to an antenna and for receiving an alternating voltage from the antenna;   a rectifier circuit coupled to the input, the rectifier circuit operable for rectifying the alternating voltage;   a shunt coupled to the rectifier and operable for regulating the rectified voltage; and   a second regulator circuit coupled to the shunt and operable for receiving the shunt current and using the shunt current to output a first regulated voltage.   
     
     
         2 . The circuit of  claim 1 , where the input is coupled to a tuning circuit for tuning the antenna. 
     
     
         3 . The circuit of  claim 1 , where the shunt includes a shunt voltage regulator circuit operable for outputting a second regulated voltage. 
     
     
         4 . The circuit of  claim 3 , where the shunt voltage regulator circuit includes a current mirror including two transistors having respective gates coupled to a control signal for controlling flow of the shunt current. 
     
     
         5 . The circuit of  claim 3 , where the second regulated voltage is applied across the antenna through the input. 
     
     
         6 . The circuit of  claim 3 , where the first regulated voltage is regulated to have a smaller voltage swing than the second regulated voltage. 
     
     
         7 . The circuit of  claim 3 , further comprising one or more switches included in the shunt voltage regulator circuit, the one or more switches biased for shunting excess shunt current to ground. 
     
     
         8 . The circuit of  claim 1 , where the second regulator circuit is a series voltage regulator circuit. 
     
     
         9 . The circuit of  claim 8 , further comprising one or more switches included in the series voltage regulator circuit, the one or more switches biased for controlling an amount of charge transferred to a second voltage supply rail. 
     
     
         10 . The circuit of  claim 1 , further comprising:
 a timer circuit operable for compensating for different currents from the shunt.