HENRIC-HUGEUX

2.4GHz AM Modulator 4 AE SE

EMCA lab report

(Study and modelling of active components)

2.4GHz AM Modulator

HENRIC Arnaud and HUGEUX François

Prepared for : Etienne Sicard and Sonia Bendhia

HENRIC-HUGEUX

2.4GHz AM Modulator 4 AE SE

Table of content Introduction .................................................................................................................... - 1 -

Carrier ............................................................................................................................. - 1 -

I. Basic oscillator ..................................................................................................... - 1 - Structural diagram .................................................................................................... - 1 - Microwind design ..................................................................................................... - 2 - Results....................................................................................................................... - 2 -

I. Voltage Controle Oscillator .................................................................................. - 2 - Structural diagram .................................................................................................... - 3 - Microwind design ..................................................................................................... - 3 - Results....................................................................................................................... - 4 -

II. Shaping filter ........................................................................................................ - 4 - First solution ............................................................................................................. - 4 - Second solution ........................................................................................................ - 5 - Results....................................................................................................................... - 5 -

Modulation ..................................................................................................................... - 6 -

I. Modulation test ................................................................................................... - 6 - Conception ................................................................................................................ - 6 - Results....................................................................................................................... - 6 -

II. Microwind design ................................................................................................. - 7 - Analogue modelling .................................................................................................. - 7 - Digital modelling ....................................................................................................... - 8 -

III. Other solution ...................................................................................................... - 8 - Analogue modelling .................................................................................................. - 9 - Digital modelling ....................................................................................................... - 9 -

Conclusion ..................................................................................................................... - 10 -

Table of illustrations ..................................................................................................... - 11 -

Bibliography .................................................................................................................. - 11 -

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Introduction

In order to put into practice the knowledge we acquired during our fourth year in automatism and electronics at INSA about modelling active components, we conducted a ten-hour study.

Our plan consisted in designing an AM modulator with a frequency of 2.4GHz. In order to achieve this, we’ve had to produce an oscillator at the frequency needed to get our carrier, then design the AM modulator. This modulator could be used to convey data via an antenna (not shown in this document). A second twosome worked on demodulation concurrently with our study.

The software Microwind as well as the book « Basics of CMOS Cell Design » have been our support to conduct this study.

Carrier

I. Basic oscillator An oscillator can be easily designed by putting in series an odd number of logic gates NOT devised from N-MOS and P-MOS transistors then by connecting the last logic gate’s output to the input of the first one. By taking into consideration the time it takes the signal to spread through the logic gates, we obtain an oscillator. Its frequency will be adjustable by two means: by increasing the signal’s propagation time through the transistors, that’s to say by increasing the width of the gate, or by adjusting the number of gates put in series, always maintaining an odd number. The diagram below illustrates the operation of the oscillator and its realization:

Structural diagram

Figure 1 : Invert oscillator’s structural diagram

VCC

Q1PMOSFET

Q2NMOSFET

Q11PMOSFET

Q12NMOSFET

Q21PMOSFET

Q22NMOSFET

Out

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2.4GHz AM Modulator 4 AE SE ~ - 2 - ~

Microwind design

Figure 2 : Invert oscillator’s Microwind design

Results

Figure 3 : Invert oscillator’s results

This signal’s frequency is 35GHz; therefore this oscillator could be used in our study. There is one problem though: its frequency is not simply adjustable, it would then be quite hard to design since we need one particular frequency (2.4GHz).

I. Voltage Controle Oscillator We therefore chose to design a VCO based on this technology, using an electronic circuit diagram by Ms. Sonia Bendhia published in the book « Basics of CMOS Cell Design ».

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Structural diagram

Figure 4 : VCO structural diagram

QD1 and QD2 will have a greater Wc compared to the other transistors in order to optimize the VCO’s oscillation.

Microwind design

Figure 5 : VCO’s Microwind design The DC voltage “Vplage”, allows us to characterize a bandwidth of oscillations among which the DC voltage Vanal is used to define more precisely the frequency we want. Sortie_VCO is the oscillator’s output while Sortie_MEF stands for the output, shaped by an inverter circuit to get a square signal.

VCC

Q1PMOSFET

QD1NMOSFET

Q11PMOSFET

Q12NMOSFET

Q21PMOSFET

Q22NMOSFET

Sortie_MEF

Q1PMOSFET

Q2NMOSFET

Q31PMOSFET

Q32NMOSFET

Q41PMOSFET

QD2NMOSFET

Q51PMOSFET

Q52NMOSFET

QS1PMOSFET

QS2NMOSFET

Sortie_VCO

Vanal

Vplage

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Results

Figure 6 : VCO results

II. Shaping filter

Once our oscillating signal obtained, we decided to shape it in order to get a sinusoidal carrier. To achieve this, we chose to use a RC filter on our VCO’s output in order to keep only the first harmonic of our signal.

First solution

Figure 7 : first filtering

S_Filtré stands for the signal once it has been filtered by the RC filter. Unfortunately, an impedance incompatibility between our two structures makes the signal useless.

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Second solution To solve this problem, we have had to adapt our filter to the oscillator impedance. We thus kept only one capacitor and used the resistor of the inverter circuit.

Figure 8 : Second filter

Results

Figure 9 : Second filter’s results

The filtering was still not optimal, but we couldn’t increase the value of the capacitor since it would have damaged our signal. We thus decided to keep this circuit to generate our carrier.

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Modulation The modulation is usually carried out by multiplying the modulating signal and the carrier. As for us, we tried to use a simple transistor by connecting the carrier to the source and the modulating signal to the gate. The modulated signal should then be measurable on the drain.

I. Modulation test To test our idea, we designed a single transistor. To the source we connected a sinusoidal voltage “sinus1” with a 2.4GHz frequency signal to simulate our carrier and to the gate another sinusoidal voltage “sinus2” with a 10MHz frequency to simulate an analogue modulating signal.

Conception

Figure 10 : MOS Modulator

Results

Figure 11 : MOS modulator results

This kind of modulation seems quite conclusive therefore we decided to keep it for the modulation of our study.

Q3NMOSFETSinus 2

Sinus 1

out

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II. Microwind design We adjusted this circuit to our carrier in order to get this design :

We tested our modulation with a analogue modulating signal and then a digital one and got the following results:

Analogue modelling

Figure 13 : Analogue modulation’s result with analogue signal

Figure 12 : Microwind design of an analogue modulator

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Digital modelling

Figure 14 : Analogue modulation’s result with digital signal

This king of modulation is working well as an analogue modulating signal. However, as a digital modulating signal it is not optimal. Indeed, when zeroing the modulating signal, the output voltage becomes floating because it is not connected to the ground. It therefore keeps its former value which can imply a low logic level at 1V.

III. Other solution We thus decided to design a second circuit to pull down the voltage when the modulating signal is at a low logic level:

Figure 15 : Digital modulator

Q4PMOSFET

Q5NMOSFET

Q6NMOSFET

Porteuse

Modulant

-Modulant

Out

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2.4GHz AM Modulator 4 AE SE ~ - 9 - ~

Analogue modelling

Figure 16 : Digital modulation’s result with analogue signal

Digital modelling

Figure 17 : Digital modulation’s result with digital signal

This circuit produce a high quality digital modulation. However, if we use an analogue signal as modulating signal, we notice a deformation of the carrier due to impedance compatibility between the modulating circuit and the oscillator. To solve this problem, we need an operational amplificatory circuit, but it would to too complicated to design it at the frequency of 2.4GHz. We thus decided to keep both of our circuits, each one being fitted for one king of modulation.

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Conclusion This study was for us the opportunity to discover a new aspect of semi-conductors through a practical experiment: the influence of components’ size on circuits’ behaviour. What’s more, thanks to our teachers, we stepped into an electronic chip designer’s shoes which enabled us to experience some issues new to us, electronics engineer students.

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Table of illustrations Figure 1 : Invert oscillator’s structural diagram ..................................................................... - 1 - Figure 2 : Invert oscillator’s Microwind design ...................................................................... - 2 - Figure 3 : Invert oscillator’s results ........................................................................................ - 2 - Figure 4 : VCO structural diagram .......................................................................................... - 3 - Figure 5 : VCO’s Microwind design ......................................................................................... - 3 - Figure 6 : VCO results ............................................................................................................. - 4 - Figure 7 : first filtering ............................................................................................................ - 4 - Figure 8 : Second filter ........................................................................................................... - 5 - Figure 9 : Second filter’s results ............................................................................................. - 5 - Figure 10 : MOS Modulator .................................................................................................... - 6 - Figure 11 : MOS modulator results ........................................................................................ - 6 - Figure 13 : Analogue modulation’s result with analogue signal ............................................ - 7 - Figure 12 : Microwind design of an analogue modulator ...................................................... - 7 - Figure 14 : Analogue modulation’s result with digital signal ................................................. - 8 - Figure 15 : Digital modulator ................................................................................................. - 8 - Figure 16 : Digital modulation’s result with analogue signal ................................................. - 9 - Figure 17 : Digital modulation’s result with digital signal ...................................................... - 9 -

Bibliography SICAR, E., & BENDHIA, S. (2007). Basics of CMOS Cell Design. Tata McGraw-Hill Education.