Temperature responsive transmitter

• US 4,689,621 A
• Filed: 03/31/1986
• Issued: 08/25/1987
• Est. Priority Date: 03/31/1986
• Status: Expired due to Fees

• Current Assignee: The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: United States Of America As Represented By The Administrator Of The National Aeronautics And Space Administration
• Inventors: Kleinberg, Leonard L.
• Primary Examiner(s): Caldwell, Sr., John W.
• Assistant Examiner(s): FATAHI YAR, MAHMOUD
• Application Number:
  US06/846,426
• Time in Patent Office: 512 Days
• Field of Search: 340/870.16, 340/870.17, 340/573, 340/384 E, 128/631, 128/736, 128/903, 331/66, 331/116 R, 331/113 R, 309/310
• US Class Current: 340/870.17
• CPC Class Codes: A61B 5/0008 Temperature signals
• CPC Class Codes: G01K 7/32 using change of resonant frequency of a crystal

Abstract

A temperature responsive transmitter is provided in which frequency varies linearly with temperature. The transmitter includes two identically biased transistors connected in parallel. A capacitor, which reflects into the common bases to generate negative resistance effectively in parallel with the capacitor, is connected to the common emitters. A crystal is effectively in parallel with the capacitor and the negative resistance. Oscillations occur if the magnitude of the absolute value of the negative resistance is less than the positive resistive impedance of the capacitor and the inductance of the crystal. The crystal has a large linear temperature coefficient and a resonant frequency which is substantially less than the gain-bandwidth product of the transistors to ensure that the crystal primarily determines the frequency of oscillation. A high-Q tank circuit having an inductor and a capacitor is connected to the common collectors to increase the collector current flow which in turn enhances the radiation of the oscillator frequency by the inductor.

Claims

1. An ingestible size temperature responsive transmitter comprising:

a plurality of transistors having commonly directly connected base, collector, and emitter electrodes;

circuit means connected to said transistors and to a pair of terminals connectable to an unidirectional voltage source for identically biasing said transistors, said circuit means including a first resistance connected between said terminals and to said base electrodes at an intermediate point and a second resistance connected between one of said terminals and said emitter electrodes;

a first capacitor connected in parallel with said second resistance;

a crystal connected between said intermediate point and the one terminal, said crystal having a resonant frequency substantially one-fourth the gain-bandwidth product of said transistors to thereby establish the oscillatory frequency when the magnitude of the absolute value of the negative resistance generated by said first capacitor is less than the positive resistive impedance of the resonant circuit effectively formed by said crystal and said first capacitor; and

a tank circuit composed of an inductance and a second capacitor connected between the other of said terminals and said collector electrodes.

2. The transmitter of claim 1 wherein said tank circuit has a high-Q to increase the collector current flow to thereby enhance the radiation of the oscillator frequency by said inductance.

3. The transmitter of claim 1 wherein said transistors are npn transistors.

4. The transmitter of claim 1 wherein said crystal has a large linear temperature coefficient.

5. The transmitter of claim 1 wherein the quiescent point of said transistors established by said circuit means is constant to thereby enhance frequency stability.

6. An ingestible size temperature responsive oscillator comprising:

a plurality of transistors having commonly directly connected base, collector, and emitter electrodes;

circuit means connected to said transistors and to a pair of terminals connectable to an unidirectional voltage source for identically biasing said transistors, said circuit means including a first resistance connected between said terminals and to said base electrodes at an intermediate point, a second resistance connected between one of said terminals and said emitter electrodes, and a third resistance connected between the other of said terminals and said collector electrodes;

a capacitor connected in parallel with said second resistance; and

a crystal connected between said intermediate point and the one terminal, said crystal having a resonant frequency substantially one-fourth the gain-bandwidth product of said transistors to thereby establish the oscillatory frequency when the magnitude of the absolute value of the negative resistance generated by said capacitor is less than the positive resistive impedance of the resonant circuit effectively formed by said crystal and said capacitor.

7. The oscillator of claim 6 wherein the quiescent point of said transistors established by said circuit means is constant to thereby enhance frequency stability.

8. The oscillator of claim 6 wherein said transistors are npn transistors.

9. The oscillator of claim 6 wherein said crystal has a large linear temperature coefficient.