NARROW BAND INTERMEDIATE FREQUENCY AMPLIFIER

• US 3,585,519 A
• Filed: 10/16/1969
• Issued: 06/15/1971
• Est. Priority Date: 10/16/1969
• Status: Expired due to Term

• Current Assignee: Kenneth Burgess
• Original Assignee: Kenneth Burgess
• Inventors: Burgess, Kenneth
• Application Number:
  US04/866,809
• Time in Patent Office: 607 Days
• US Class Current: 330/306
• CPC Class Codes: H03F 3/191 Tuned amplifiers H03F3/193, H03F3/195 take precedence

Abstract

A narrow band intermediate frequency (IF) amplifier having three stages coupled by double-tuned filters, each stage including a semiconductor amplifying element that is biased and loaded to give a slightly negative output resistance with a voltage protective diode in each stage, the protective diode in the last stage being a hot-carrier diode to provide low intermodulation distortion at high input signal levels between stages thereby producing output IF of narrow 3 decibels (db.) bandwidth for frequency modulation (FM) circuits.

Claims

1. A narrow band intermediate frequency amplifier for frequency modulation circuits comprising:

a plurality of transistor amplifiers each biased and loaded to produce an output resistance slightly negative;

double-tuned filters with inputs and outputs connected to establish interstage couplings for said plurality of transistor amplifiers to provide impedance matching and frequency band shaping of conducted signals; and

a diode in parallel with the output of each filter to protect each succeeding transistor amplifier from voltage overloads, said diode in the output of the filter of the last stage being a hot-carrier diode to provide a low limiting threshold voltage and a narrow bandwidth of output signal frequencies whereby intermediate frequency signals for frequency modulated circuits are amplified to produce a low 3 decibels bandwidth with minimum intermodulation distortion.

2. A narrow band intermediate frequency amplifier as set forth in claim 1 wherein said double-tuned filters are transformers having a resistor and a capacitor in parallel across the primary winding and two capacitors in series across the secondary winding in parallel with said diode, the input to said coupling double-tuneD transformer filter being to one lead of said primary winding and the output being taken from the junction of said two capacitors in series whereby each of said primary windings and each of said secondary windings are tuned and filtered.

3. A narrow band intermediate frequency amplifier as set forth in claim 2 wherein said transistor amplifiers are each of base controlled NPN type and each said diode is oriented to limit positive going voltage signals.

4. A narrow band intermediate frequency amplifier as set forth in claim 3 wherein each said transistor amplifier has said interstage coupling input to the base electrode and includes a capacitor coupled between said base electrode and the emitter electrode through a base biasing resistance to minimize ground loop and to insure stability in the amplifier.