EMCA lab report. (Study and modelling of active components) HENRIC-HUGEUX. HENRIC Arnaud and HUGEUX François

Transcription

1 EMCA lab report (Study and modelling of active components) HENRIC Arnaud and HUGEUX François Prepared for : Etienne Sicard and Sonia Bendhia 4 AE SE

2 Table of content Introduction Carrier I. Basic oscillator Structural diagram Microwind design Results I. Voltage Controle Oscillator Structural diagram Microwind design Results II. Shaping filter First solution Second solution Results Modulation I. Modulation test Conception Results II. Microwind design Analogue modelling Digital modelling III. Other solution Analogue modelling Digital modelling Conclusion Table of illustrations Bibliography AE SE

3 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. I. Basic oscillator Carrier 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 VCC Q1 Q11 Q21 Q2 Q12 Out Q22 Figure 1 : Invert oscillator s structural diagram 4 AE SE ~ ~

4 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». 4 AE SE ~ ~

5 Structural diagram VCC Q1 Q1 Q11 Q21 Vanal Q2 QD1 Q12 Q22 Q31 Q41 Q51 QS1 Vplage Q32 QD2 Q52 Sortie_VCO Sortie_MEF QS2 Figure 4 : VCO structural diagram QD1 and QD2 will have a greater W c compared to the other transistors in order to optimize the VCO s oscillation. Microwind design Figure 5 : VCO s Microwind design The DC voltage V plage, allows us to characterize a bandwidth of oscillations among which the DC voltage V anal 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. 4 AE SE ~ ~

6 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. 4 AE SE ~ ~

7 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. 4 AE SE ~ ~

8 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 Sinus 1 Sinus 2 Q3 Figure 10 : MOS Modulator out 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. 4 AE SE ~ ~

9 II. Microwind design We adjusted this circuit to our carrier in order to get this design : Figure 12 : Microwind design of an analogue modulator 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 4 AE SE ~ ~

10 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: -Modulant Porteuse Q5 Q4 Out Modulant Q6 Figure 15 : Digital modulator 4 AE SE ~ ~

11 Analogue modelling Digital modelling Figure 16 : Digital modulation s result with analogue signal 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. 4 AE SE ~ ~

12 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. 4 AE SE ~ ~

13 Table of illustrations Figure 1 : Invert oscillator s structural diagram Figure 2 : Invert oscillator s Microwind design Figure 3 : Invert oscillator s results Figure 4 : VCO structural diagram Figure 5 : VCO s Microwind design Figure 6 : VCO results Figure 7 : first filtering Figure 8 : Second filter Figure 9 : Second filter s results Figure 10 : MOS Modulator Figure 11 : MOS modulator results Figure 13 : Analogue modulation s result with analogue signal Figure 12 : Microwind design of an analogue modulator Figure 14 : Analogue modulation s result with digital signal Figure 15 : Digital modulator Figure 16 : Digital modulation s result with analogue signal Figure 17 : Digital modulation s result with digital signal Bibliography SICAR, E., & BENDHIA, S. (2007). Basics of CMOS Cell Design. Tata McGraw-Hill Education. 4 AE SE ~ ~