Multiple amplifier interconnection for optimal sensitivity

• US 4,434,405 A
• Filed: 04/19/1982
• Issued: 02/28/1984
• Est. Priority Date: 04/19/1982
• Status: Expired due to Term

• Current Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Original Assignee: Bell Telephone Laboratories, Inc. (Nokia Corporation)
• Inventors: Gans, Michael J., Snell, William W. Jr.
• Primary Examiner(s): Mullins, James B.
• Application Number:
  US06/369,497
• Time in Patent Office: 680 Days
• Field of Search: 330/84, 330/149, 330/124 R, 330/295
• US Class Current: 330/149
• CPC Class Codes: H03F 1/26 Modifications of amplifiers to reduce influence of noise generated by amplifying elements
• CPC Class Codes: H03F 2200/372 Noise reduction and elimination in amplifier
• CPC Class Codes: H03F 3/68 Combinations of amplifiers, e.g. multi-channel amplifiers for stereophonics power amplifiers using a combination of several semiconductor amplifiers H03F3/211; combinations of amplifiers using coupling networks with distributed constants H03F3/602

Abstract

To obtain optimal operational sensitivity from an amplifier connected to a source of electrical signals, a technique utilizes multiple amplifiers connected together. The technique determines the number, N, of amplifiers (31 or 51) to be used and whether they should be connected in parallel (FIG. 3) or series (FIG. 5) in order to optimize the sensitivity of a given type of amplifier. Accordingly, multiple interconnection of amplifiers may be used in lieu of noise matching with transformers to minimize the excess-noise figure of the multiple amplifier circuit. The technique capitalizes on the advances in integrated circuit amplifier design, such as compactness and wideband performance, while providing lower loss and higher reliability through redundancy.

Claims

1. A low noise circuit for providing amplified electrical signals comprising

a source of electrical signals including a predetermined source resistance R_g

characterized in that

a plurality of N like amplifiers are connected together, each amplifier includes a predetermined rms noise voltage E_R and a predetermined rms noise current I_R ;

and

the plurality of N like amplifiers are connected in series, where N is substantially equal to the quantity (I_R R_g)/E_R, for R_g greater than E_R /I_R.

2. A low noise circuit in accordance with claim 1 further comprising output means for providing a common output node, said output means resistively coupled individually to each of the outputs of the plurality of N amplifiers.

3. A low noise source for providing amplified electrical signals produced by a source of electrical signals including a predetermined source resistance R_g, the low noise circuit comprising:

a plurality of N-like amplifiers, each amplifier including a predetermined rms noise voltage E_R and a predetermined rms noise current I_R wherein the plurality of N-like amplifiers have their inputs serially connected together when the value of R_g is greater than E_R /I_R and the value of N is approximately equal to the quantity of (I_R R_g)/E_R.

4. A low noise circuit according to claim 3 further comprising output means for providing a common output node, the output means comprising a plurality of N resistors each having one terminal connected to the node and the other terminal connected to the output of one of the N amplifiers.