GB2307141A

GB2307141A - Switching Regulator for GSM Mobile

Info

Publication number: GB2307141A
Application number: GB9522638A
Authority: GB
Inventors: John Charles Duncan
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-11-04
Filing date: 1995-11-04
Publication date: 1997-05-14
Also published as: GB9522638D0

Abstract

A switching regulator booster 2 is directly applicable for use in GSM Mobile hand-held units. The switching regulator is turned off during required windows (eg: the transmit window) to eliminate interference at the transmitter output. Power is supplied to the required circuits (eg: the power amplifier) by stored charge in capacitors 4 of sufficient capacitance. It thus becomes possible to run a GSM mobile hand-held from a single cell Li-ion battery or a series correction of ordinary 1.2 volt cell low cost batteries.

Description

SWITCHING REGULATOR FOR TELECOMMUNICATIONS APPARATUS One of the important aims in both analogue and digital mobile communications is to reduce the weight, dimension and volume of the hand-held unit.

Through integration it has become possible to reduce the weight and dimensions of the electronic components and it is the batteries that now limit further size and weight reductions. It is generally necessary to use four cell battery packs to achieve about 5 volts. Most electronic devices can be operated at lower voltages than 5 volts but it is the Power Amplifier in hand-held units that cannot be operated at voltage levels below about 4.3 volts. Two Watt Global System for Mobile Communications (GSM) handheld units employ Power Amplifiers (PA's) which can only operate with voltage levels greater than 4.3 volts. This exceeds what is possible to obtain from a three cell battery pack which provides a nominal voltage level of 3.6 volts.

It is possible to up-convert a lower voltage level with reasonable efficiency using a switched mode power supply converter, however this causes problems particularly in GSM hand-held units due to the presence of switching frequencies on the regulated output voltage. These switching frequencies on the regulated output of the switchingup converter cause undesirable sidebands at the transmitter output of a GSM handheld unit and this results in the unit failing the GSM Type Approval specifications.

The invention described here solves this problem and enables a switched mode supply system to be used to up-convert a Direct Current (DC) level supplied from a 3 cell (or less) battery pack which is free from the interference of the switching frequencies inherent in the design of switched mode power supplies.

Figure 1 describes the invention. The switching regulator up-convertor2 is an off-theshelf device with an Enable input 6. In Figure 1, box 2 represents the up-convertor together with some external components such as inductors, capacitors and resistors for the functioning of the off-the-shelf regulator.

The battery 1 is the low voltage battery, either in a series combination of 1.2 volt cells or a single cell Li-ion battery with a terminal voltage of 3 .6Volts.

The required up-converted and regulated output voltage is obtained from point 5. The diode 3 is a requirement in up convertors to isolate the higher voltage at 5 from the rest of the regulator. The capacitor 4 is the smoothing capacitor which improves regulation at 5.

A switching regulator has generally internal switching frequency of about 100 kHz and the frequency and products of it couple to 5 and it is not easy to filter them out completely.

Because GSM is a Time Division Multiple Access (TDMA) system, the transmitter is turned on only 1 time slot of approximately 0. 57milli second in a period of about 4.5 milli second as shown in Figure 2.

If the transmitter Power Amplifier is connected to 5 then the switching frequency will generate undesirable sidebands and spurii at the PA output.

According to the present invention, the switching regulator booster is disabled by means of a suitable control signal applied to the enable port of the regulator booster so that the switching waveforms are not active during the GSM transmit period. In such a state, diode 3 isolates point 5 (the power amplifier voltage supply port) from the regulator 2 and it is the charge stored in the capacitor 4 which suplies the required voltage to the PA Capacitor 4 needs to be large enough to supply the demand of the PA even in the highest power conditions. The capacitor 4 will be discharged partially during the transmit window but the booster will be enabled immediately after the transmit window to enable the booster to charge up the capacitor 4 to the correct level before the next transmit window.

Claims

1 A switching regulator booster employing a control signal to turn off the switching regulator booster off during GSM transmit window and on during the rest of the GSM TDMA frame to convert battery voltages from typical values such as 1.2, 2.4, and 3.6 volts to a level such as Svolts suitable for power amplifiers in GSM hand-held apparatus.

2 A large value capacitor to store sufficient charge to supply the power amplifier voltage during GSM transmit window.

3 Facility to switch on and off the up convertor booster during other GSM windows such as the receive window.