Telephone interface circuit

• US 20080037772A1
• Filed: 07/06/2006
• Published: 02/14/2008
• Est. Priority Date: 07/06/2006
• Status: Active Grant

• Current Assignee: Uniden Corporation (Cornwall Capital Management LP)
• Original Assignee: Uniden Corporation (Cornwall Capital Management LP)
• Inventors: Fujiwara, Yoshinobu
• Granted Patent: US 7,940,922 B2
• Time in Patent Office: Days
• US Class Current: 379/442
• CPC Class Codes: H04M 1/738 Interface circuits for coupling substations to external telephone lines H04M1/78 takes precedence

Abstract

A telephone interface circuit comprising a speech circuit, a control circuit turning on upon receiving a supply of a forward direction trigger current so as to connect first and second telephone lines and the speech circuit, and going off upon receiving a supply of a reverse direction trigger current so as to disconnect the first and second telephone lines and the speech circuit, a capacitor charging and discharging charge supplied from the first telephone line, and a hook switch supplying charge accumulated at the capacitor when off-hook to the control circuit as a forward direction trigger current, and supplying charge discharged from the capacitor when on-hook to the control circuit as a reverse direction trigger current.

Claims

1. A telephone interface circuit comprising:

a speech circuit;

a control circuit turning on upon receiving a supply of a forward direction trigger current so as to connect first and second telephone lines and the speech circuit, and going off upon receiving a supply of a reverse direction trigger current so as to disconnect the first and second telephone lines and the speech circuit;

a capacitor charging and discharging charge supplied from the first telephone line; and

a hook switch supplying charge accumulated at the capacitor when off-hook to the control circuit as a forward direction trigger current, and supplying charge discharged from the capacitor when on-hook to the control circuit as a reverse direction trigger current.

2. The telephone interface circuit of claim 1, wherein the control circuit is a thyristor.

3. The telephone interface circuit of claim 1, wherein the control circuit is a Schmitt trigger.

4. The telephone interface circuit of claim 2, wherein the thyristor comprises a first transistor, second transistor, and feedback circuit;

a base terminal of the first transistor and a collector terminal of the second transistor are connected;

an emitter terminal of the first transistor is connected to the first telephone line;

a collector terminal of the first transistor branches into two, with one branch being connected to the speech circuit and the other branch being connected to the positive feedback circuit;

a base terminal of the second transistor branches into two, with one branch being connected to the positive feedback circuit and the other branch being connected to the capacitor;

an emitter terminal of the second transistor branches into two, with one branch being connected to the speech circuit and the other branch being connected to the second telephone line; and

the hook switch connects the capacitor and the first telephone line when off-hook, and connects the capacitor and the second telephone line when on-hook.

5. The telephone interface circuit of claim 4, the positive feedback circuit comprising a speed-up capacitor for shortening turn-on time of the second transistor.