Diode receiver for radio frequency transponder

• US 5,889,489 A
• Filed: 10/17/1996
• Issued: 03/30/1999
• Est. Priority Date: 08/31/1995
• Status: Expired due to Term

• Current Assignee: Intermec IP Corporation (Honeywell International Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Friedman, Daniel Joseph, Heinrich, Harley Kent
• Primary Examiner(s): Lobo, Ian J.
• Application Number:
  US08/733,684
• Time in Patent Office: 894 Days
• Field of Search: 342/51, 342/44, 340/825.54, 340/825.69
• US Class Current: 342/51
• CPC Class Codes: G01S 13/758 using a signal generator powered by the interrogation signal
• CPC Class Codes: G06K 19/0701 at least one of the integrated circuit chips comprising an arrangement for power management
• 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

Abstract

A passive radio frequency transponder (RF tag) having a diode rectifier receiver circuit outside the tag power rectification circuit, the tag power rectification circuit supplying power to the electronics of the RF tag. An additional innovative low current circuit protect the signal capacitor from overvoltage produced by the signal diode. An innovative circuit also clips the signal and sharpens it. An innovative low current circuit is used as a comparator to sharpen the signal pulses.

Claims

1. A passive radio frequency (RF) transponder (tag), comprising;

a tag antenna for receiving RF power and modulated RF information signal sent to the tag by a base station;

a tag voltage rectification power circuit attached to the tag antenna, the tag voltage rectification power circuit for receiving RF power from the antenna and for providing power to tag electronics, the tag electronics receiving power only from the tag voltage rectification power circuit; and

a tag voltage rectification receiver circuit separate from the tag voltage rectification power circuit, the voltage rectification receiver circuit for receiving modulated RF signals from the antenna and for providing demodulated information signals to the tag electronics, wherein the tag voltage rectification receiver circuit comprises;

an RF diode, a first terminal of the RF diode attached to a first terminal of the antenna;

a signal capacitor attached between a second terminal of the RF diode and a second terminal of the antenna, and;

a transistor current drain connected in parallel to the signal capacitor.

2. The RF tag of claim 1, wherein the transistor current drain limits the current drained from the signal capacitor to a defined current.

3. The RF tag of claim 1, wherein the transistor current drain is an n channel transistor connected as an n mirror transistor.

4. The RF tag of claim 1, wherein the signal capacitor is protected against overvoltage by a low current protection circuit connected in parallel with the signal capacitor.

5. The RF tag of claim 4, wherein the low current protection circuit draws less than 50 nA when there is no overvoltage on the signal capacitor.

6. The RF tag of claim 1, wherein an instantaneous voltage on the signal capacitor is compared to a moving average of the instantaneous voltage on the signal capacitor.

7. The RF tag of claim 6, wherein the signal capacitor is shorted out when the instantaneous voltage on the signal capacitor is significantly less than the moving average of the instantaneous voltage on the signal capacitor.

8. The RF tag of claim 1, wherein the signal capacitor is shorted out when the tag electronics detects a falling edge on the signal on the signal capacitor.

9. The RF tag of claim 8, further comprising a signal capacitor shorting circuit comprising;

a high current transistor connected in parallel with the signal capacitor; and

an edge detection circuit which generates a spike on falling edges detected on the signal at the second terminal of the RF diode, the spike output of the edge detection circuit connected to the gate of the high current transistor.

10. A passive radio frequency (RF) transponder (tag), comprising;

a tag antenna for receiving RF power and modulated RF information signals sent to the tag by a base station;

a tag voltage rectification power circuit attached to the tag antenna, the tag voltage rectification power circuit for receiving RF power from the antenna and for providing power to tag electronics, the tag electronics receiving power only from the tag voltage rectification power circuit; and

a tag voltage rectification receiver circuit separate from the tag voltage rectification power circuit, the voltage rectification receiver circuit for receiving modulated RF signals from the antenna and for providing demodulated information signals to the tag electronics, wherein the tag voltage rectification receiver circuit comprises;

an RF diode, a first terminal of the RF diode attached to attached to a first terminal of the antenna;

a signal capacitor attached between a second terminal of the RF diode and a second terminal of the antenna, wherein the signal capacitor is protected against overvoltage by a low current protection circuit connected in parallel with the signal capacitor, and wherein the low current protection circuit comprises;

a high current transistor connected in parallel with the signal capacitor;

a first and a second low current transistor connected in series, each transistor having a different saturation current, the first and a second low current transistor connected in series being connected in parallel with the signal capacitor, wherein a voltage at the connection between the first and a second low current transistor controls the high current transistor to carry high current to protect the signal capacitor during overvoltage conditions, and to carry very little current in a condition of no overvoltage and;

a transistor current drain connected in parallel to the signal capacitor.

11. A passive radio frequency (RF) transponder (tag), comprising;

a tag antenna for receiving RF power and modulated RF information signals sent to the tag by a base station;

a tag voltage rectification power circuit attached to the tag antenna, the tag voltage rectification power circuit for receiving RF power from the antenna and for providing power to tag electronics, the tag electronics receiving power only from the tag voltage rectification power circuit; and

a tag voltage rectification receiver circuit separate from the tag voltage rectification power circuit, the voltage rectification receiver circuit for receiving modulated RF signals from the antenna and for providing demodulated information signals to the tag electronics, wherein the tag voltage rectification receiver circuit comprises;

an RF diode, a first terminal of the RF diode attached to a first terminal of the antenna;

a signal capacitor attached between a second terminal of the RF diode and a second terminal of the antenna, wherein an instantaneous voltage on the signal capacitor is compared to a moving average of the instantaneous voltage on the signal capacitor and;

a transistor current drain connected in parallel to the signal capacitor;

further comprising a moving average comparison circuit comprising;

a series connected first and a second transistor connected in parallel with the signal capacitor, the first transistor with its drain connected to the gate and drain of the second transistor, the gate of the first transistor connected to a mirroring reference voltage, the source of the first transistor connected to the second terminal of the antenna, and the source of the second transistor connected to the second terminal of the RF diode;

an averaging capacitor connected between the drain of the first transistor and the second terminal of the antenna; and

a series connected third and a fourth transistor connected in parallel with the signal capacitor, the third and the fourth transistor having different saturation currents, the gate of the third transistor connected to the gate of the first transistor, the drain of the third transistor connected to the drain of the fourth transistor, the source of the third transistor connected to the second terminal of the antenna, the gate of the fourth transistor connected to the gate of the second transistor, and the source of the fourth transistor connected to the second terminal of the RF diode.

12. A passive radio frequency (RF) transponder (tag), comprising;

a tag antenna for receiving RF power and modulated RF information signals sent to the tag by a base station;

a tag voltage rectification power circuit attached to the tag antenna, the tag voltage rectification power circuit for receiving RF power from the antenna and for providing power to tag electronics, the tag electronics receiving power only from the tag voltage rectification power circuit; and

a tag voltage rectification receiver circuit separate from the tag voltage rectification power circuit, the voltage rectification receiver circuit for receiving modulated RF signals from the antenna and for providing demodulated information signals to the tag electronics, wherein the tag voltage rectification receiver circuit comprises;

an RF diode, a first terminal of the RF diode attached to attached to a first terminal of the antenna;

a signal capacitor attached between a second terminal of the RF diode and a second terminal of the antenna, wherein an instantaneous voltage on the signal capacitor is compared to a moving average of the instantaneous voltage on the signal capacitor and;

a transistor current drain connected in parallel to the signal capacitor;

further comprising a moving average comparison circuit comprising;

a series connected first and a second transistor connected in parallel with the signal capacitor, the drain of the first transistor connected to the gate and drain of the second transistor, the gate of the first transistor connected to a mirroring reference voltage, the source of the first transistor connected to the second terminal of the RF diode, and the source of the second transistor connected to the second terminal of the antenna;

an averaging capacitor connected between the drains of the first 2 transistors and the second terminal of the RF diode;

a series connected third and a fourth transistor connected in parallel with the signal capacitor, the third and the fourth transistor having different saturation currents, gate of the third transistor connected to the gate of the first transistor, the drain of the third transistor connected to the drain of the fourth transistor, the source of the third transistor connected to the second terminal of the RF diode, the gate of the fourth transistor connected to the gate of the second transistor, and the source of the fourth transistor connected to the second terminal of the antenna.