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PD54008L: 8W-7V LDMOS in PowerFLAT packages for wireless meter reading applications

Posted: 29 Nov 2004     Print Version  Bookmark and Share

Keywords:POWER 

/ARTICLES/2004NOV/A/2004NOV29_RFD_POW_AN.PDF

1. ABSTRACT

In the last years STMicroelectronics has been strongly involved in finding new package solutions for

power integrated circuits to get a totally Surface Mount Device (SMD).

The PowerFLATTM case introduced in this application note shows the new concept of chip-size

packaging representing a fundamental step to reduce the costs of assembly and to shrink power

amplifier modules.

This package helps maximize board space with improved electrical and thermal performances over

traditional leaded packages.

This leadless package is an MLP (Micro Leadframe Package) where the electrical connections are made

through lands on the bottom surface of the component. These lands are soldered directly to the pc

board.

Figure 1: MLP Cross-section

The standard MLP has an exposed die attach pad which enhances the thermal and electrical

characteristics enabling high power and high frequency applications.

For small and medium power applications, such as wireless PMR (Private Mobile Radio) LDMOS

(Laterally Diffused MOS) transistors in PowerFLAT packages offer certain advantages compared to

equivalent bipolar transistors, for example:

7 BETTER INTERMODULATION (IMD3)

Under certain conditions, an LDMOS transistor exhibits better intermodulation distortion than a bipolar

junction transistor. Figure 2 shows intermodulation distortion versus peak effective output power for

equivalently rated bipolar and LDMOS transistors.

As we can see, below 30W, the LDMOS device has lower intermodulation distortion than the bipolar

transistor.

October 2004 1/11

AN2048

APPLICATION NOTE

PD54008L: 8W-7V LDMOS in PowerFLAT packages

for wireless meter reading applications

AN2048 - APPLICATION NOTE

2/11

Figure 2: Intermodulation Distortion versus Peak Effective Output Power

7 GOOD GAIN LINEARITY

7 SMOOTH SATURATION

7 SIMPLER BIAS CIRCUIT

7 THERMAL STABILITY

The drain current has a positive temperature coefficient; therefore the MOS transistor is not

susceptible to thermal run-away.

7 BETTER RUGGEDNESS

2. BASIC WIRELESS METER READING SYSTEM DESCRIPTION

To reduce cost and difficulties associated with the reading of indoor utility meters for gas, water and

electric, a new automatic meter reading system has recently been introduced. It uses radio frequency

networks and allows a direct data communication between reading meters and services and/or billing

department.

A DTU (Data Transmission Unit) module that contains a powerful UHF narrow-band radio transmitter is

attached to gas, water and electric utility meters.

Figure 3: Network System

AN2048 - APPLICATION NOTE

.

3/11

A DCU (Data Collector Unit) is placed in a convenient location within an apartment, building or housing

complex.

Each day, the DCU contacts a NCC (Network Control Computer) and forwards the meter reading

information.

The NCC processes the information and provides billing data and customer support information.

This paper describes a DTU unit solution using an STMicroelectronics 8W - 7V LDMOS device housed in

a PowerFLAT and called PD54008L.

3. ELECTRICAL REQUIREMENTS

VDD=5V IDQ = 10mA Frequency Band [450-:-470] MHz

Pout = 36dBm Gain flatness < 1dB

4. CIRCUIT DESIGN AND CONSIDERATIONS

PD54008L is an 8W - 7V LDMOS housed in a PowerFLAT plastic package (5x5mm).

Being an internally unmatched device, the PD54008L can be used in different portable applications over

HF, VHF&UHF frequency bands.

Table 1 shows the source and load impedances of PD54008L at 500 MHz.

Figure 4: Source and Load Impedances of PD54008L

Table 1: Source and Load Impedances of PD54008L at 500 MHz

The above impedances will be taken as a starting point to design the input and output matching networks

of the PD54008L amplifier. Microstrip lines & lumped elements will be used.

4.1 AMPLIFIER CONSTRUCTION

The PCB is made of two-side copper clad fiberglass (THK 0.020") with the lowest dielectric constant

(r = 2.17) and dissipation factor available.

The printed circuit board is glued to a copper for dissipation purposes.

F(MHz) Z1(ohms) Z2(ohms)

500 1.3+j2.0 1.8+j0.7

AN2048 - APPLICATION NOTE

4/11

Figure 5: Device's Footprint

Figure 6: Cross-section

4.2 CIRCUIT SCHEMATIC AND COMPONENTS LIST

Figure 7: Broadband Power Amplifier

AN2048 - APPLICATION NOTE

.

5/11

Table 2: Components List

4.3 TRANSMISSION LINE

The microstrip layout (gerber files available on request) is shown below.

Figure 8: Transmission Line

AN2048 - APPLICATION NOTE

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5. CHARACTERIZATION RESULTS

After tuning for the best performance the results are as shown in figure 9.

Figure 9: Power Gain vs Frequency

Figure 10: Input Return Loss vs Frequency

PD54008L

0

2

4

6

8

10

12

14

16

445 448 451 454 457 460 463 466 469 472 475

F(MHz)

G(dB)

Po=36dBmIdq=10mA

PD54008L

-10

-8

-6

-4

-2

0

445 448 451 454 457 460 463 466 469 472 475

F(MHz)

RL(dB)

Po=36dBmIdq=10mA

AN2048 - APPLICATION NOTE

.

7/11

Figure 11: Drain Efficiency vs Frequency

Figure 12: Drain Efficiency vs Frequency at Different Drain Voltages

PD54008L

0

10

20

30

40

50

60

70

80

90

100

445 448 451 454 457 460 463 466 469 472 475

F(MHz)

Eff.(%)

Idq=10mA Po=36dBm

PD54008L

0

10

20

30

40

50

60

70

80

90

100

445 448 451 454 457 460 463 466 469 472 475

F(MHz)

EFF(%)

VDD=5V

VDD=7.5V

VDD=9V

Pin=24.5dBm

Idq=10mA

AN2048 - APPLICATION NOTE

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Figure 13: Power Out vs Drain Voltage at Different Frequencies

After the electrical analysis, the PD54008L was removed from the pcb and the input/output impedances

were measured.

Figure 14: Input/output Impedance

PD54008L

0

5

10

15

20

25

30

35

40

45

1 2 3 4 5 6 7 8 9 10

VDD(V)

Pout(dBm)

F=445MHz

F=460MHz

F=475MHz

Pin=24.5dBm

Idq=10mA

F(MHz) Z1(ohms) Z2(ohms)

450 1.0+j2.9 1.8+j0.5

460 0.9+j3.0 1.9+j0.7

470 0.9+j3.4 1.9+j0.9

AN2048 - APPLICATION NOTE

.

9/11

6. COMPONENTS LAYOUT

Figure 15: PCB Layout

Figure 16: Picture of PD54008L Amplifier

7. CHARACTERIZATION RESULTS

As we can see from figures 9, 10 & 11, we can achieve a minimum gain of 12 dB with an input return loss

better than 5dB and a drain efficiency between 55% and 65% over the frequency band 445-:-475 MHz.

Even so the output power can be controlled thru Vgs, a minimum of 15 dB dynamic range can be

achieved by varying Vdd (fig. 13). This allows a better control of the transmitted power out and may

extend the transmission range capability of more than 3 miles (depending on environment) as requested

in some commercial product.

AN2048 - APPLICATION NOTE

10/11

8. FEATURE CHARACTERISTICS

It is useful to show other optional functions where to employ this application:

7 Equipment monitoring;

7 CO/Methane/Fire detection;

7 Security/Alarm services;

7 Data logging;

7 All VHF & UHF PMR portables.

REFERENCES

1. Steve C. Cripps "RF power amplifiers for wireless communications", Artech House

2. Bill Travis - "RF transistors meet wireless challenges" - Technical Editor - EDN magazine pag. 53 -

61, May 3, 2001 - www.ednmag.com.

3. Juhel S. - Hamelin N. "PowerSO-10RF - The first true RF power SMD Package" - Application Note

1294 - STMicroelectronics.

4. Pritiskutch J. - Hanson B. "Understanding LDMOS device fundamentals" Application Note 1226 -

STMicroelectronics.

AN2048 - APPLICATION NOTE

.

11/11

Information furnished is believed to be accurate and reliable. However, STMicroelectronics assumes no responsibility for the consequences

of use of such information nor for any infringement of patents or other rights of third parties which may result from its use. No license is granted

by implication or otherwise under any patent or patent rights of STMicroelectronics. Specifications mentioned in this publication are subject

to change without notice. This publication supersedes and replaces all information previously supplied. STMicroelectronics products are not

authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics.

The ST logo is a registered trademark of STMicroelectronics.

All other names are the property of their respective owners

) 2004 STMicroelectronics - All rights reserved

STMicroelectronics group of companies

Australia - Belgium - Brazil - Canada - China - Czech Republic - Finland - France - Germany - Hong Kong - India - Israel - Italy - Japan -

Malaysia - Malta - Morocco - Singapore - Spain - Sweden - Switzerland - United Kingdom - United States of America

www.st.com





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