Browse Prior Art Database

METHOD FOR ALC

IP.com Disclosure Number: IPCOM000006974D
Original Publication Date: 1993-Jun-01
Included in the Prior Art Database: 2002-Feb-13
Document File: 2 page(s) / 102K

Publishing Venue

Motorola

Related People

Tat Mor: AUTHOR [+2]

Abstract

In a bipolar transistor circuits, many important parameters are dependent on the AC level at the base- emitter junction. Such parameters include phase noise, harmonic content, output power etc.

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MOTOROLA INC. Technical Developments Volume 19 June 1993

METHOD FOR ALC

by Tat Mor and Gadi Shirazi

PROBLEM SOLVED BY THE INVENTION:

  In a bipolar transistor circuits, many important parameters are dependent on the AC level at the base- emitter junction. Such parameters include phase noise, harmonic content, output power etc.

  In circuits that are sensitive to component variation, it is common to use automatic level control (ALC) to keep the circuit's output constant. However, traditional ALC circuits include many additional components, which may s.utTer from their own variation. Moreover the tra- ditional ALC circuits monitor the output of the circuit and not the level on the junction, which often is more important to control than the output (for example iftight control of harmonics is necessary).

DESCRIPTION OF THE INVENTION

  Circuits that may benefit from the proposed ALC arc large signal bipolar circuit. These include oscillators, frequency multipliers, frequency converters etc.

  The proposed ALC makes use of the phenomenon of "depression voltage" present on the PN junction under large AC excitation. This makes the DC voltage on the junction dependent on the amplitude of the AC signal on the junction, reducing the voltage as the AC ampli- tude is increased.

  This phenomenon is described in detail in Clarke and Hess's "Communication circuits: analysis and design" pp 1 through 4. The value given for the depression volt- age is V = Vq - 6V where 6V is given by: Vt*ln(Ig(x)).*

Moreover, at high enough levels, 6V approaches the value of Vat (peak).

   It is, therefore, possible to know the AC level on the junction by simply monitoring the DC voltage on the junction, this may be done without loading the circuit

*X denotes Va, (peak)/Vt

by connecting large resistors or inductors to the base and emitter. (ii one of the leads is grounded we may use only one connection.)

  An ALC circuit may then be designed with its con- trolled parameter being the DC voltage. No extra detec- tors and buffers are needed.

  For increased accuracy across the temperature range, a similar transistor with equal DC bias and no AC applied may be used as a reference.

  The same method may be used for trimming dur- ing production process. For example, laser trimming of bias resistors on a hybrid oscillat...