Low level RF threshold detector
First Claim
1. A circuit for selectively activating RF equipment upon detection of an RF activation signal, comprising:
- a means for receiving the activation signal to be detected;
an RF detector operatively connected to the receiving means;
a means for supplying a threshold reference level signal;
a converting means operatively connected to the RF detector for converting the output of the RF detector from a dc voltage signal to a square wave signal having a polarity opposite that of the threshold reference level signal;
an ac-coupled limiting amplifier having as its input the combined output of the converting means and the signal from the threshold reference supply; and
a means for detecting the phase of the amplifier output and comparing it to the phase of the threshold reference level signal, and activating the RF equipment when the phase of the amplifier output is opposite the phase of the threshold reference level signal.
17 Assignments
0 Petitions
Accused Products
Abstract
A low power circuit which detects low level RF signals and RF signals of varying strength and, upon detection, activates or "wakes up" RF equipment, such as an automatic vehicle identification tag, that is normally kept in a dormant state to conserve operating power between active operations. The circuit converts a detected RF signal from a dc voltage signal to an ac voltage signal by "chopping" the dc signal to a "chopped dc" square wave, the amplitude of which is proportional to that of the original dc signal voltage, which in turn is proportional to the level of the received RF signal. The chopped dc square wave is then linearly combined with a threshold reference level signal of opposite polarity and the combined signals form the input to an ac-coupled limiting amplifier. The polarity of the amplified signal is identical to that of the larger of its two input signals. A phase detector determines the polarity of the amplified signal. When the phase detector discerns the detected RF activation signal, it activates the RF equipment.
31 Citations
8 Claims
-
1. A circuit for selectively activating RF equipment upon detection of an RF activation signal, comprising:
-
a means for receiving the activation signal to be detected; an RF detector operatively connected to the receiving means; a means for supplying a threshold reference level signal; a converting means operatively connected to the RF detector for converting the output of the RF detector from a dc voltage signal to a square wave signal having a polarity opposite that of the threshold reference level signal; an ac-coupled limiting amplifier having as its input the combined output of the converting means and the signal from the threshold reference supply; and a means for detecting the phase of the amplifier output and comparing it to the phase of the threshold reference level signal, and activating the RF equipment when the phase of the amplifier output is opposite the phase of the threshold reference level signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
-
Specification