Design and optimization of a RF module for a Xbox game controller

using VBA

● Joost ter Laak● Consultant● Joost.ter.Laak@jtl-engineering.nl

RF module in Xbox applications● Wanted is a RF module to enable a

wireless transmission to a Xbox console– Game controller– Headset– etc.

Module demands● Operates in 2.40-2.48 GHz ISM band● A few dBm output power● About -92 dBm sensitivity● Cheap to build● Easy to build using simple SMD

components (R,C)● Uses LMX4281 from SiTel Semiconductor

Module schematic

LNA

PA

Antenna

LMX4281

BalunsInterconnect

Filter

Interconnect

Bias

Open loopVCO

Equivalent circuit for lna balun

1 2

1 2

3 4MUC2ID=M1L1=1.15 nHL2=4.04 nHK1_2=1

1

2

SUBCKTID=S4NET="lna_4281_data"

PORTP=2Z=50 Ohm

0 1.0

1.0

-1.0

10.0

1 0 . 0

-10.0

5.0

5 . 0

-5.0

2.0

2 .0

-2.0

3.0

3 .0

-3.0

4.0

4 .0

-4.0

0.2

0.2

- 0 . 2

0.4

0.4

- 0. 4

0.6

0.6

- 0. 6

0.8

0.8

- 0.8

lna_impedanceSwp Max6000MHz

Swp Min100MHz

2440 MHzr 50 Ohmx 0 Ohm

2440 MHzr 19 Ohmx -55 Ohm

S(1,1)Differential mode

S(2,2)Transformed

LNA balun

Gap

Track width

Width

Length

Offset

How to come to a layout● What is an optimal layout

– How small can it be– Trade Area between RF circuits and

antenna – Grounding– Unwanted radiation/coupling to VCO

I have no layout without a simulation.

Foresee some iterations ==>need for a flexible layout

PCB vs MWS layout

● Normal flow: start from PCB layout ==> optimize in MWS ==> change PCB

● Unsure what to parametrize

● Solution: build layout with a VBA macro such that everything can be parametrized

Macro creates layout● Layout can be optimized for hexahedral

meshing● Easy to create only individual parts● Easy to parametrize

VBA macro● Constants which could become a parameter● Functions to facilitate● Subroutines to create the RF parts● Subroutines to set environment/mesh/ports etc.● Flags to choose layout options

Constants

Comment out and makeit a parameter

Routines to Facilitate

Example, routine to place via's in a track

Create RF partsComment calls out ifonly a part is needed.

For example onlyAntenna

SMD component tuning● Generate Layout, simulate, export

touchstone to circuit simulator

RF parts

25 mm

16 mm

Bended Inverted F antenna

Pa balun, matching and biasing

Lna balun andmatching

LMX4281, RF IC

Interconnect

Antenna● Not enough space for dipole● Bended Inverted F ● Radiation pattern chosen to correct for the

attenuation by the hands

Antenna

E

H

Radiation pattern

Pattern corrects for the position of the hands.

Antenna impedance

Red is simulated

Green is measured

Summary● VBA enabled all kind of layout explorations● Measurements and simulations agree● Module is used in mass production