Contactless ic card system

Abstract

In a contactless IC card system, a modulating circuit manufactured in an IC form is operable at a high power efficiency. The demodulating apparatus is configured to include: first signal output means for outputting a first output signal having a predetermined phase with respect to that of an input signal, a second signal output means for outputting a second output signal having a predetermined phase with respect to that of the input signal, gate means for gating at least the second output signal, calculation means for adding, or subtracting the first output signal and the second output signal; and control means for controlling the operation of the gate means in response to a logic level of input data.

1 . A communication apparatus, comprising:
 carrier signal input means for inputting a carrier signal;   first signal output means for outputting a first output signal having a first predetermined phase with respect to said carrier signal;   second signal output means for outputting a second output signal having a second predetermined phase with respect to said carrier signal;   gate means for gating at least said second output signal;   operation means for operating said first output signal and said second output signal;   transmitting means for transmitting an output signal of said operation means using an antenna; and   control means for controlling the gate means by outputting a control signal to said gate means.   
   
   
       2 . A communication apparatus as claimed in  claim 1 , wherein
 the first output signal has a same phase as that of the input signal; and   the second output signal has a phase opposite to that of the input signal.   
   
   
       3 . A communication apparatus as claimed in  claim 1 , wherein
 the first signal output means power-amplifies the first output signal to output a power-amplified first output signal; and   said second signal output means power-amplifies said second output signal to output a power-amplified second output signal.   
   
   
       4 . A communication apparatus as claimed in  claim 1 , wherein said input signal is a sine wave signal having a single frequency. 
   
   
       5 . A communication apparatus as claimed in claim  23 , wherein said input signal is a rectangular wave signal having a single frequency. 
   
   
       6 . A communication apparatus as claimed in  claim 5 , wherein said second signal output means outputs said second output signal having a phase opposite to that of said input signal by inverting the logic level of said input signal. 
   
   
       7 . A communication apparatus as claimed in  claim 3 , wherein
 said gate means controls a stopping of the power amplifying operation by said second signal output means so as to gate said second output signal; and   said second signal output means maintains an impedance of an output terminal at a high impedance for a time period during which the power amplifying process operation is stopped.   
   
   
       8 . A communication apparatus as claimed in  claim 3 , wherein at least one of said first output signal means and said second output signal means provide its respective power-amplified output signal to a switching circuit for switching operations in response to said input signal. 
   
   
       9 . A communication apparatus as claimed in  claim 3 , wherein at least said second signal output means and said gate means are tri-state buffer circuits.