Browse Prior Art Database

CARRIER SIGNAL PATTERN DEMODULATOR

IP.com Disclosure Number: IPCOM000009838D
Original Publication Date: 2000-May-01
Included in the Prior Art Database: 2002-Sep-23
Document File: 4 page(s) / 174K

Publishing Venue

Motorola

Related People

Michael Burri: AUTHOR

Abstract

A method of detecting data in an electronic reader interface, received from a contact less smart card or tag transponder, in which the reader supplies power to the contact less card or transponder via a radio frequency transmit loop antenna. The same transmit antenna is also used to receive back scattered signal from the card or tag device which is perfonned with an admittance load switching device inside the card device.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 37% of the total text.

MOTOROLA

Technical Developments

CARRIER SIGNAL PATTERN DEMODULATOR

by Michael Burri

BACKGROUND

A method of detecting data in an electronic reader interface, received from a contact less smart card or tag transponder, in which the reader supplies power to the contact less card or transponder via a radio frequency transmit loop antenna. The same transmit antenna is also used to receive back scattered signal from the card or tag device which is perfonned with an admittance load switching device inside the card device.

The transmitted data from the card can be modulated directly on the carrier or on sub-carrier. The rate of the modulated data is synchronized with the internal frequency generating the carrier frequency.

Different type of modulation schemes may be used which have to be decoded to obtain the NRZ data infonnation.

THE SOLUTION

The design proposed is a ROM pattern demodulator capable of detecting different schemes of digital signals shown in Figure 1. For instance, BPSK and OOK signals can be detected and demodulated taking into account their characteristics such as the mark/space ratio and of the fact that they can be coded in Manchester for instance. Also, a certain amount of noise disturbing the pattern of the signal can be predetermined allowing the demodulator to extract the data information.

Synchronized Sampling Clock

Incoming Encoded Signal

Shift Register

ROM

Signal Status Outputs

Fig. 1 ROM Pattern Demodulator

Figure 2 shows the electrical diagram of the Pattern demodulator configured to decode BPSK/OOK signals. BPSK means Bi-Phase Shift Keying. Bi-Phase means they are two conditions which will specify the data bit information lor 0 and Shift Keying is defined by shifting of the carrier signal by 180 degrees each time the data information bit changes its status from O to lor 1 to 0.

The Figure 3 shows the wave fonn of modulated data at 107 kBaud rate. The demodulated data has a constant output delay of one period of the carrier signal related to the modulated input signal.

Motorola, Inc. 2000

Different Baud rate can be demodulated theoretically up to the half of the frequency of the incoming encoded signal.

OOK means On Off Keying. The carrier is ON (active) or Off (not active).

In the example, shown in Figure 3, the BPSK/OOK signals have been encoded on a 847.5kHz carrier frequency and are input to the 8bit Shift Register which is clocked at 3.39MHz.

Thus, the sampling resolution is 4 samplings for one period of the carrier signal. The parallel out-

148

May 2000

MOTOROLA

Technical Developments

847.5 kHz encoded signa[s

D 8 bit Shift Reg C

3.39 MHz

A7 A6A5A4A3A2A 1 AO DO 01 02 03 04 05 06 07

ROM

DEMODULATED BPSK

RS FF BPSR

SIGNAL PATTERN OK

NOISE (ev. trend to O or to 1} IDLE at -1IDLE at -0SUB-CARRIER ACTIVE .. .. MCU

.,......""""....""""", "...."".."""""",

, ,

, ,

, ,

, ,

,

~ Q R C 3.39 MHz ~ ~ n n-bit counter ~

, ,

, I I I , ftw I

~"" , .., 'S..~f..'S.." " , ~'} ,~, !~..e,c ,~~~y ,~, ,,~!~;

RS FF OOK DEMOOULATEOOOK

Fig. 2 ...