High impedance signal detection device

• US 4,852,152 A
• Filed: 10/19/1987
• Issued: 07/25/1989
• Est. Priority Date: 10/19/1987
• Status: Expired due to Term

• Current Assignee: Neptune Technology Group Incorporated (Roper Technologies, Inc.)
• Original Assignee: 501 Neptune Information Systems
• Inventors: Honick, Ronald J.
• Primary Examiner(s): Ng, Jin F.
• Assistant Examiner(s): Chan, Wing F.
• Application Number:
  US07/109,857
• Time in Patent Office: 645 Days
• Field of Search: 379/107, 379/106, 379/97, 379/98, 379/413, 379/104
• US Class Current: 379/93.05
• CPC Class Codes: H04M 11/002 with telemetering systems telemetering in general G08C
• CPC Class Codes: Y10S 331/02 Phase locked loop having lock indicating or detecting means

Abstract

A low power consuming signal detection device for attachment to a telephone line. The device has an impedance of at least five megohms across the telephone lines. The device includes a power supply having an input impedance of least five megohms and an amplifier powered by the power supply for amplifying tone interrogation signals present on the telephone line. A phase-locked-loop is responsive to the amplifier signals for determining when the frequency of the amplified signals are within a predefined bandwidth. Phase locking of the phase-locked-loop to the amplified signals is detected by a lock detector when the frequency of the signals falls within a predetermined bandwidth for a predetermined period of time. the lock detection signal is used to place meter reading circuitry in an "off-hook" condition and for effecting the transfer of data from meter data collection apparatus over the telephone line back to a remote location. The signal detection device is solely powered by the normal telephone central office power supply which is applied to the telephone line. Circuitry is provided for temperature compensating the phase-locked-loop to provide a relatively stable source of reference signals for the phase-locked-loop.

Claims

1. A high impedance telephone line signal detection device powered by a telephone line in an on-hook condition, comprising:

means for supplying power within the detection device with an impedance of at least 5 megohms across the telephone line;

means for amplifying a signal having at least one predetermined frequency on the telephone line, the amplifying means being AC-coupled to the telephone line with an impedance such that the impedance across the telephone line of said power supply means and said amplifying means together is at least 5 megohms;

phase-locked-loop signal sensing means, powered by said power supply means, for determining when the frequency of said signal amplified by said amplifying means is within a predefined bandwidth;

lock detection means for outputting a control signal when the frequency of said amplified signal from the telephone line is within said predefined bandwidth for a predetermined period of time; and

said power supply means comprises a junction field effect transistor with a gate-to-source cutoff voltage of sufficient level to supply power to operate said phase-locked-loop signal sensing means and said lock detection means.

2. The detection device of claim 1, wherein said junction field effect transistor has a gate-to-source cutoff voltage between 3.0 and 3.8 volts.

3. The detection device of claim 2, wherein said phase-locked-loop signal detection means comprises CMOS integrated circuitry.

4. The detection device of claim 2, wherein said resistor of at least 5 megohms resistance is in series between the telephone line and the drain of said junction field effect transistor.

5. The detection device of claim 1, wherein the phase-locked-loop signal sensing means comprises a voltage controlled oscillator means, including resistive and capacitive components, for generating a reference signal whose frequency is inversely proportional to the RC value of said components.

7. The detection device of claim 5, wherein said voltage controlled oscillator comprises means for compensating for temperature variations in order to minimize frequency variations in the reference signal.

8. The detection device of claim 7, wherein said temperature compensation means comprises a varicap diode as a capacitive component of the voltage controlled oscillators such that as the temperature increases, the capacitance of the varicap diode increase, tending to lower said oscillator'"'"'s frequency in compensation of the tendency of an increase in temperature to cause the remainder of the oscillator to increase its frequency.

9. The detection device of claim 8 wherein said varicap diode is in the portion of the circuit which determines the frequency of said oscillator.

10. The detection device of claim 1, wherein said means for supplying power has an impedance of at least 10 megohms.

6. The detection device of claim 6, wherein said resistive components have a resistance of a least 5 megohms and said capacitive components have complementary values to generate said reference signal frequency.

11. A telephone line signal detection device which is powered by a telephone central office battery, comprising:

means for amplifying signals on the telephone line;

means for generating a stable reference voltage and for converting said voltage to a proportional frequency of oscillation;

means for comparing the frequency of said amplified telephone line signals to said frequency of oscillation and generating a control signal when the difference between the two frequencies falls within a preselected range; and

means, which draws less than 5.0 microamperes of current, for converting telephone line battery potential to a supply voltage, wherein said converting means comprises a junction field effect transistor with a gate-to-source cutoff voltage of sufficient level to supply said supply voltage to operate said amplifying means, said reference voltage generating means, and said frequency comparing means.