Browse Prior Art Database

REVERSE BIASED SENSING SCHOTTKY DIODE

IP.com Disclosure Number: IPCOM000008956D
Original Publication Date: 1999-Jan-01
Included in the Prior Art Database: 2002-Jul-26
Document File: 2 page(s) / 78K

Publishing Venue

Motorola

Related People

Khoo Soo Hee: AUTHOR

Abstract

Power slumping of a power amplifier (PA) on portable radios is a problem that occurs even with the use of either a Power Sense or Current Sense ALC circuitry. Such power slumping is due to the PA heating up with continuous keying of a radio. A sensing schottky diode circuit is proposed to com- pensate for this drop and thereby alleviate power slumping as such.

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M-LA Technical Developments

REVERSE BIASED SENSING SCHOTTKY DIODE

by Khoo Soo Hee

INTRODUCTION

  Power slumping of a power amplifier (PA) on portable radios is a problem that occurs even with the use of either a Power Sense or Current Sense ALC circuitry. Such power slumping is due to the PA heating up with continuous keying of a radio. A sensing schottky diode circuit is proposed to com- pensate for this drop and thereby alleviate power slumping as such.

DESCRIPTION

  In a typical Power Sense ALC, a programmed current, I,,, is compared with the current detected at the Coupler, to generate the control voltage (V,) needed to set the output power. The circuit of Figure 1 on next page shows part of a typical ALC at the current comparator transistor, Ql. The pro- grammed current, shown as I,,c, comes from a DAC. The problem is that the ALC circuit is rela- tively sensitive with the I,,c not more than a few tens of microamps at most. Connected to the base of the transistor is the proposed circuit.

  The compensation circuit utilizes a Schottky barrier diode, CRl, operated in reverse bias, the reverse bias voltage, V, is determined by biasing resistors, Rl and R2. Cl and C2 are bypass capaci- tors. The diode acts as the temperature sensing device and is placed closed to the PA.

  When operated in reverse bias, there is a small but constant reverse leakage current flowing through the diode. This leakage current is not constantly over temperature but increases steadily at higher...