Circuit arrangement of a reading device for electromagnetic identification cards

• US 4,782,308 A
• Filed: 03/06/1987
• Issued: 11/01/1988
• Est. Priority Date: 03/07/1986
• Status: Expired due to Fees

• Current Assignee: ISKRA-SOZD ELEKTROKOVINSKE INDUSTRIJE N.SOL.O., TRG REVOLUOIJE 3, YU-61000 LJUBLJANA
• Original Assignee: Iskra-Sozd Elektrokovinske Industrije N.Sol.O.
• Inventors: Zivlakovic, Marko, Trobec, Franc, Erzen, Vital, Zmavc, Joze, Rozman, Miro
• Primary Examiner(s): Grimm, Siegfried H.
• Application Number:
  US07/022,691
• Time in Patent Office: 606 Days
• Field of Search: 331/65, 331/167, 331/DIG. 3, 331/158, 340/505, 340/542, 340/552, 340/825.31, 340/825.34, 340/825.54, 340/825.55, 340/825.72, 324/57 Q, 324/236, 361/182, 235/380, 235/381, 235/382, 235/382.5
• US Class Current: 331/65
• 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
• CPC Class Codes: G06K 7/086 sensing passive circuit, e.g. resonant circuit transponders

Abstract

A circuit arrangement of a reading device for electromagnetic identification cards having inverters connected in parallel and an LC resonant circuit forming a transmitting oscillator which is influenced by the identification card to change the amplitude of an oscillating signal in order to recognize approach thereto of the card. Detection of the signal amplitude change is utilized to form pulses for subsequent data processing in which the influence of distance between the identification card and the reading device is minimized.

Claims

1. A circuit arrangement of a device for reading electromagnetic identification cards, comprising an oscillator (1, 1'"'"', 1"), a detector (2) and a pulse-forming circuit (3), said oscillator including a resonance circuit having a resistor (R_o, R) a capacitor (C_o, C_o '"'"', C5) and a coil L_o, L_o '"'"', L1) operatively interconnected in series and parallel connected inverters (I1, I2, I3, I, I1'"'"', I2'"'"', I3'"'"') connected to the resistor, said inverters respectively having inputs and outputs, and capacitor means (C, C6) for interconnecting the inputs and outputs of the inverters with ground, said detector including a first coupling capacitor (C1) connected to said inverters of the oscillator, a grounded diode (D1), and coupling diode (D2), a first junction interconnecting the grounded diode and the coupling diode with said coupling capacitor, a first grounded capacitor (C2), a first grounded resistor (R1) and a second junction interconnecting the first grounded capacitor and the first grounded resistor with said coupling diode, said pulse-forming circuit including a second coupling capacitor (C3) connected to the second junction of the detector, a comparator (K) having positive and negative inputs and an output, a pair of resistors (R3, R4) respectively connected to said positive and negative inputs, a third junction interconnecting said pair of resistors with the second coupling capacitor, a second grounded resistor (R2) connected to said third junction, a second grounded capacitor (C4) connected to the negative input, a feedback resistor (R5) interconnecting the positive input and the output of the comparator, an output terminal (5) and a plurality of inverters (I4, I5, I6) interconnected in parallel between the output of the comparator and the output terminal.

2. The circuit arrangement of claim 1, including a quartz crystal (Q) connected in parallel with the resistor (R) and the inverters (I1, I2, I3) of the oscillator (1'"'"'), a plurality of additional inverters (I1'"'"', I2'"'"', I3'"'"') having inputs connected in parallel to the outputs of the first mentioned inverters and outputs connected in parallel to the detector and in series with the capcitor (C_o '"'"') and the coil (L_o '"'"') of the resonance circuit.

3. The circuit arrangement of claim 1 including a quartz crystal (Q) connected in parallel with the resistor (R) and one of the inverters (I) of the oscillator (1"), said capacitor means (C) of the oscillator interconecting the input and output of said one of the inverters to ground, the other of the inverters (I1'"'"', I2'"'"', I3'"'"') being interconnected in parallel between the output of said one of the inverters and the detector and in series with the coil (L1) and the capcitor (C5) of the resonance circuit and means for capacitively adjusting the capacitor of the resonance circuit, said capacitor means including a fourth junction between the adjustable capacitor of the resonance circuit and the first coupling capacitor (C1) of the detector and a grounded capacitor (C6) connected to said fourth junction.

4. A device for reading an electromagnetic card, comprising oscillator means for generating a signal at a frequency tuned to said card, detector means connected to the oscillator means for detecting a predetermined change in amplitude of the frequency tuned signal in response to inductive coupling between the card and the oscillator means and pulse-forming circuit means connected to the detector means for producing a readable output in response to said detection of the change in signal amplitude, said oscillator means including a resonance circuit through which the oscillator means is inductively coupled to the card, signal inverting means connected to the resonance circuit for transmitting the generated signal to the detector means and capacitor means for coupling the signal inverting means to ground.

5. The reading device as defined in claim 4 wherein said pulse-forming circuit means includes an output terminal, a comparator having a pair of inputs and an output, coupling means for separately connecting said inputs to the detector means, a feedback resistor interconnecting one of the inputs and the output of the comparator and signal inverting means for connecting the output of the comparator to the output terminal.