Browse Prior Art Database

POWER CONTROL IN A TDD SYSTEM

IP.com Disclosure Number: IPCOM000008403D
Original Publication Date: 1997-Dec-01
Included in the Prior Art Database: 2002-Jun-12
Document File: 4 page(s) / 186K

Publishing Venue

Motorola

Related People

Randall Hillock: AUTHOR

Abstract

In a TDD system the radio transmits and receives on the same frequency. The transmission and reception are offset in time. Depending on the band of operation and regulatory concern, there exists a need for monitoring and controlling the power output of the transmission. For some PCS systems being employed at 1.9 GHz power accuracy is being specified at +l/-3 dB. In the ISM band the FCC specifies max E.R.I.P. of 36 dBm. For portable equipment operating at 100 mW power level one would not need power control to meet this regulatory requirement. However, to optimize coverage and performance it would be an advantage to keep out- put power as consistent over frequency and supply voltage as possible.

This text was extracted from a PDF file.
At least one non-text object (such as an image or picture) has been suppressed.
This is the abbreviated version, containing approximately 36% of the total text.

Page 1 of 4

MOTOROLA Technical Developments

POWER CONTROL IN A TDD SYSTEM

by Randall Hillock

  In a TDD system the radio transmits and receives on the same frequency. The transmission and reception are offset in time. Depending on the band of operation and regulatory concern, there exists a need for monitoring and controlling the power output of the transmission. For some PCS systems being employed at 1.9 GHz power accuracy is being specified at +l/-3 dB. In the ISM band the FCC specifies max E.R.I.P. of 36 dBm. For portable equipment operating at 100 mW power level one would not need power control to meet this regulatory requirement. However, to optimize coverage and performance it would be an advantage to keep out- put power as consistent over frequency and supply voltage as possible.

  Data was taken on a 3.3 V 2.45 GHz 200 mW PA and the power variation across the frequency band 2.4 GHz to 2.5 GHz and over a ten percent supply variation resulted in i 2.5 dB power change from nominal conditions. These characteristics are dependent upon the PA and how far into saturation the device is being driven. If the power window of +l/-3 dB is to be met, power control must be employed. However, due to cost and power

constraints, introducing any additional loss after the PA or components to the radio is not desirable. Figure I is a transceiver proposed for a 2.4 GHz wireless data system. The goal is to implement power control without introducing any additional components or loss after the PA and make use of the existing hardware required to implement the radio.

  The transceiver is Figure 1 consists of a main PLL at 2163-2263 MHz and a 237 MHz PLL, which the 2nd LO signal and Offset signals are derived from. During transmission, due to finite isolation between the PA output and the down mixer, an IF signal is generated at the down mixer output. During reception and transmission the injec- tion signal at 2163-2263 MHz and at - 5 dBm is always present at the down mixer. To implement power control in this transceiver it is necessary to make use of the fact that an IF signal is being generated during transmission and to use the RSSI feature of the ZlF to make a power estimate of the transmission. The analog RSSI signal is fed into an g-bit A/D for reception reasons. This hardware will be used for electronic tuning of power out.

11 Mot"r"lr. Inc. ,997 34 December 1997

[This page contains 15 pictures or other non-text objects]

Page 2 of 4

0 M

MOTOROLA Technical Developments

@ 237 MHz -IOdBlllRXON -45 dBm Rx OFf

+SdBm -5dBm

2163 - 2263 MHz

-v--Q

2163 - 2263 MHaPLL

I

24W - 2500 MHz 237 MHz PLL

Fig. 1

  The diagram in Figure 1 illustrates some of the levels being generated at the down mixer output during transmission. The PA output during transmis- sion is 23 dBm. Isolation between the transmitter and receiver on the T/R switch is typically 20 dB. During transmission we measure the level of the TX signal at the LNA input to be 1 dBm. The saturated power out of the LNA a...