VITAL LEVEL DETECTOR AND "AND" GATE CIRCUIT ARRANGEMENT EMPLOYING A TWIN-TEE OSCILLATOR

• US 3,793,596 A
• Filed: 06/01/1972
• Issued: 02/19/1974
• Est. Priority Date: 06/01/1972
• Status: Expired due to Term

• Current Assignee: Union Switch & Signal, Inc. (Hitachi, Ltd.)
• Original Assignee: Reed H. Grundy
• Inventors: Grundy, Reed H.
• Primary Examiner(s): Saalbach, Herman Karl
• Assistant Examiner(s): Grimm, Siegfried H.
• Application Number:
  US05/258,879
• Time in Patent Office: 628 Days
• Field of Search: 331/65,18B,110,142,173,185,186 307/235 317/31,146 340/248B,248D
• US Class Current: 331/110
• CPC Class Codes: G08G 1/161 Decentralised systems, e.g. inter-vehicle communication
• CPC Class Codes: H03B 5/26 frequency-determining element being part of bridge circuit in closed ring around which signal is transmitted; frequency-determining element being connected via a bridge circuit to such a closed ring, e.g. Wien-Bridge oscillator, parallel-T oscillator

Abstract

This disclosure relates to a fail-safe level detecting and AND gating circuit including a multistage solid state amplifier having a regenerative feedback loop. The regenerative feedback loop includes a frequency determining twin-tee network and a pair of voltage breakdown devices. The multistage amplifier produces a.c. oscillations when and only when the level of a d.c. voltage applied across each of the voltage breakdown devices exceeds its threshold value so that both of the breakdown devices become conductive and exhibit a low impedance condition.

Claims

1. A vital circuit for producing a.c. output oscillations only upon the concurrent appearance of a first and a second d.c. input comprising, a multistage amplifier having a regenerative feedback loop, said regenerative feedback loop including a frequency selective network for determining a given frequency of oscillation, and a pair of voltage responsive devices cooperatively associated with said frequency selective network for controlling the amount of regenerative feedback occurring at the given frequency so that a.c. output oscillations are produced by the multistage amplifier when said pair of voltage responsive devices are rendered conductive by said first and said second d.c. inputs exceeding a predetermined value.

2. A vital circuit as defined in claim 1, wherein said frequency selective network comprises a twin-tee filter having a high pass portion and a low pass portion.

3. A vital circuit as defined in claim 1, wherein said frequency selective network includes a filter circuit having input, output and common impedance legs.

4. A vital circuit as defined in claim 1, wherein each of said pairs of said voltage responsive devices comprises a Zener diode.

5. A vital circuit as defined in claim 3, wherein said pair of voltage responsive devices control the impedance value of the common leg of said filter circuit.

6. A vital circuit as defined in claim 2, wherein said twin-tee circuit includes a plurality of resistors and capacitors.

7. A vital circuit as defined in claim 1, wherein said multistage amplifier includes a two-stage transistor circuit.

8. A vital circuit as defined in claim 7, wherein said feedback loop is taken from the output of the second of said two-stage transistor circuit and applied to the input of the first of said two-stage transistor circuit.

9. A vital circuit as defined in claim 7, wherein the two-stage transistor circuit includes a first stage which is connected in a common collector configuration and a second stage which is connected in a common-emitter configuration.

10. A vital circuit as defined in claim 1, wherein said frequency selective circuit comprises a twin-tee network having an input, an output and a common leg, each of said legs including a resistor and a capacitor, said resistor of said common leg is connected in series with one of said pair of said voltage responsive devices and said capacitor of said common leg is connected in series with the other of said pair of said voltage responsive devices.