Pràctica 2 (2013)Trabajo Inglés
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< CSL; Linear Circuits and Systems (Practice 2) >
Authors: Castán, Anna and Sanchez, Andrea
The purpose of this practice is to characterize the behavior of a Colpitts
oscillator. This circuit is a type of oscillator (system generates its output signal
with a sinusoidal excitation voltage continues) using a transistor and a set of
resistive elements (R) and Reactive (L and C).
3. MATERIAL PRACTICAL REALIZATION MINUMUM • A plate connections (Proto-board type).
• 1 transistor BC 107B.
• 1 resistance value R = 22 kΩ Schematic circuit Colpitts oscillator.
• 2 value capacitors C1 = C2 = 10 nF (Hard). Code 103 Ceramic Disc Capacitor • 1 bobinade 5µH (o4.7µH) • One coaxial cable with BNC connectors, banana.
• 2-wire connectors unifilars banana-banana.
• Power supply simple. • Oscilloscope.
Circuit diagram of a small signal transistor.
4. CIRCUIT ASSEMBLY 2.PRELIMINARI STUDY 2.1. Find the transfer function of the oscillator circuit H (s) = V0 (s) / IN (s).
To do this, use the equivalent circuit of Figure 3, small signal transistor model and considering that there is a current source IN modeling the noise generated by the resistor R. Applying systematic node voltages in matrix form.
4.1. Assemble the circuit plate with L = 5 µH (µH or 4.7), R = 22 kΩ, C1 = C2 = 10nF disc and transistor BC 107B.
Terminals transistor Schematic of the equivalent circuit to calculate H (s) 2.2. Imposing the condition of oscillation circuit, calculate the value of β transistor. Use the following values: β= -1.1125 4.2 Measuring the oscilloscope output voltage of the circuit and get the frequency sinusoidal signal.
2.3. Demonstrate pulse oscillation circuit ω0 can be approximated as; W0=√((C1+C2+Gi·G·L)/(C1·C2·L)) f= 1.58MHz 2.4. Find the value of the frequency f0 (Hz) f0= 1MHz < CSL; Linear Circuits and Systems (Practice 2) > 4.3 Qualitatively assess the degree of sensitivity of the oscillation frequency depending on the temperature of the capacitor (may be heated with the fingers or with a lighter better).
f= 1.898MHz 4.4 Using the FFT option of the oscilloscope, or see the frequency components of the signal spectrum.
5. CONCLUSIONS In this practice we have learned to characterize the behavior of a Colpitts oscillator. So your system generates its output signal with a sinusoidal excitation voltage. What cost us more to the study was preliminary and that is where the theory is applied to the circuit. The practical class montage circuit and measure voltages has seemed easy. We have not had any problems when doing this practice.