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A NOVEL APPROACH TO START UP ALGORITHMS IN AMPLIFIERS WITH LARGE CAPACITIVE LOADS

IP.com Disclosure Number: IPCOM000018637D
Original Publication Date: 2003-Jul-29
Included in the Prior Art Database: 2003-Jul-29
Document File: 5 page(s) / 239K

Publishing Venue

Motorola

Related People

Noel Carlos F. Carneiro: AUTHOR

Abstract

A new approach to charge a large external capacitive load, where the large external loads reduces the start up time of amplifiers, is proposed by the introduction of an auxiliary start up driver. The algorithm uses very little area and the dissipated power is increased only during a very short period of time.

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Page 1 of 5

A new approach to charge a large external capacitive load, where the large external loads reduces the start up time of amplifiers, is proposed by the introduction of an auxiliary start up driver. The algorithm uses very little area and the dissipated power is increased only during a very short period of time.

Normally, in order to reduce the start up time, large output drivers, usually transistors (MOS or bipolar, where available), are used to increase the output current that charges the external load.

Some of the problems with the use of large output drivers are:

* Increase in the area that they occupy, which is, usually, already large, and consequently, an increase in the costs;

* Increase of output current, leading to an increase in the dissipated power.

The area occupied by the output drivers, and by the dissipated power limits the problem of reducing the start up time.

So far, there is not a simple solution for reducing the start up time without complicated circuits and/or large output drivers.

In the new approach, the large current is only needed during the start up time, when

the external capacitive load needs to be charged to the desired value in a very short period of time. Otherwise, there is no need for large current, for the external capacitor can provide the circuit's current requirements. Consequently, the dissipated power is reduced.

The algorithm presented here solve this problem by proposing a novel approach to the start up problem, in which very small area is added to the circuit that implements the algorithm and the dissipated power is increase only during a very short period of time.

The large current is only needed during the start up time, when the external capacitive load needs to be charged to the desired value in a short period of time. Otherwise, there is no need for large current, for the external capacitor can provide the circuit's current requirements.

During the start up time, the inputs of the output buffer amplifier are at different voltage levels. One of the inputs is at the desired reference voltage level, while the other is connected to the output voltage, which, during the start up time, is trying to reach the desired reference voltage level.

The idea behind the proposed method is to use this voltage difference (within a certain tolerance level) to activate a current source that would work only during the start

Copyright Motorola, 2003

A NOVEL APPROACH TO START UP ALGORITHMS IN AMPLIFIERS WITH LARGE CAPACITIVE LOADS

Noel Carlos F. Carneiro

1. Abstract

3. Proposed Method

2. Introduction

Page 2 of 5

4. Example of implementation

up time, providing a large amount of current to charge the external capacitor. When the voltage difference is zero (within a certain tolerance level), the current source would not work. See Fig. 1.

The controlled current source Io is

governed by the rule:

where Von is the output of the decision

circuit and I is the required output current necessary to charge the external lo...