Transmitter apparatus and communication system employing the same

• US 7,145,960 B2
• Filed: 11/07/2002
• Issued: 12/05/2006
• Est. Priority Date: 12/27/2001
• Status: Expired due to Fees

• Current Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Original Assignee: Sharp Kabushiki Kaisha (Hon Hai Precision Industry Co., Ltd.)
• Inventors: Shigemasa, Haruhiko, Nakao, Yoshihiro
• Primary Examiner(s): Kumar, Pankaj
• Assistant Examiner(s): Ejaz, Naheed
• Application Number:
  US10/289,325
• Publication Number:
  US 20030123567A1
• Time in Patent Office: 1,489 Days
• Field of Search: 375/295, 375/363, 375/369, 375/354, 375/362, 370/503, 370/511, 370/512, 370/513, 370/514, 370/464, 370/498, 370/506, 370/509, 342/42, 342/43, 342/51
• US Class Current: 375/295
• CPC Class Codes: G06K 19/0723 the record carrier comprising an arrangement for non-contact communication, e.g. wireless communication circuits on transponder cards, non-contact smart cards or RFIDs
• CPC Class Codes: G06K 7/0008 General problems related to the reading of electronic memory record carriers, independent of its reading method, e.g. power transfer

Abstract

A transmitter apparatus has a modulator for modulating a carrier wave to produce a modulated wave having communication data superimposed thereon and a transmitter for transmitting the modulated wave to a receiver apparatus. Before starting communication, the transmitter apparatus transmits a predetermined dummy pulse to the receiver apparatus so as to bring the communication data restored by demodulation in the receiver apparatus into a logic state in which the communication data should be kept when no communication is taking place. This makes it possible to perform correct communication even if the communication data demodulated in the receiver apparatus before the start of communication is not kept in the logic state in which it should be kept when no communication is taking place.

Claims

1. A transmitter apparatus comprising:

a modulator for modulating a carrier wave to produce a modulated wave having communication data superimposed thereon; and

a transmitter for transmitting the modulated wave to a receiver apparatus,

wherein the communication data is capable of being communicated on a frame-by-frame basis, each frame including a start of frame indicator indicating a head of the frame, character data conforming to a character transmission protocol, and an end of frame indicator indicating a tail of the frame, and

before starting transmission of the communication data, the modulator superimposes a dummy pulse on the carrier wave, the dummy pulse bringing a logic state of a demodulated wave demodulated in the receiver apparatus into a logic state that is different from the start of frame indicator and in which the demodulated wave is kept when no communication is taking place.

2. A transmitter apparatus as claimed in claim 1, wherein the modulator is a circuit that produces the modulated wave having the communication data superimposed thereon by amplitude-modulating the carrier wave, and before reducing an amplitude of the modulated wave to mark the start of frame, reduces the amplitude of the modulated wave temporarily from an original level thereof and then restores the amplitude of the modulated wave to the original level.

3. A transmitter apparatus as claimed in claim 2,

wherein a degree in which the amplitude of the modulated wave is reduced temporarily is equal to a degree in which the amplitude of the modulated wave is reduced during normal modulation.

4. A transmitter apparatus as claimed in claim 2,

wherein, immediately after the amplitude of the modulated wave is reduced temporarily, the modulated wave is kept unmodulated for a period equal to or shorter than a period required to transmit one-bit data.

5. A communication system comprising:

a transmitter apparatus as claimed in claim 2; and

a receiver apparatus that demodulates the received modulated wave and, by detecting the logic transition of the resulting demodulated wave from the logic state that is different from the start of frame indicator and in which the demodulated wave is kept when no communication is taking place to a logic state corresponding to the start of frame indicator, detects the start of frame indicator and thereby recognizes a start of communication with the transmitter apparatus.

6. A communication system as claimed in claim 5,

wherein the transmitter apparatus and the receiver apparatus are a non-contact-type IC card and a reader/writer apparatus that performs data communication with the IC card.