Other Applications

The RF amplifier can be used in other systems such as the paul trap, cylindrical ion trap,the linear ion trap and the penning trap which all use amplitude modulated Rf voltage opearating about the same frequency(1-2MHz). They can be operated at low voltages and are readily used in mass spectometers to detect or analyse chemicals i.e to detect the presence of explosives in an airport .

Design and biasing

Pspice simulated circuit for our design

Gain for Pspice simulation

 The design used is a single stage amplifier and this is good because it helps keep the beta value of the transistor constant and holds the base bias at a constant voltage for better stability of the circuit. The voltage entering the transistor(Vb) is derrived from the potential divider network formed by R1 and R2 in parallel and there is a voltage drop of  0.7V in order to open the transistor junctions. A different type of design involving an inductor and a capacitor in parallel at the emitter part of the transistor could have been used but that would require very tideous work as we would have to tune the LC until the output and feedback are in phase to avoid undesired noise amplification as we are dealing with high frequencies(fixed values).Also using an LC in the circuit instead will give us small bandwidth which is not ideal in this case.

Noise

Following the design of our circuit we are starting to think about noise generated by the circuit components which may affect its output and real life functionality. Although in the simulations our design has a gain of almost 2 but in reality this will not be the case. From theory, the emitter resistor (RE) reduces the noise in our circuit and in turn increases stability of the circuit.

We have been discussing the how to test our circuit when it is built. We will pass white noise through the circuit and using our theoritical knowledge of band pass filters, check that the desired frequency range is at the output.

Useful Links And Reference Texts

NPN Common Emitter

Inductor Values

Capacitor Values

Transistor Data Sheet

Inductor data sheet

axial inductor data sheet

Ion trap types

http://www.cavehill.uwi.edu/fpas/cmp/online/EL31L/elet3120-oscillators.htm
"Electronics: A systems approach"  Neil Storey

Resonant Frequency

The Capacitor and Resistor in parallel have equal impedance at this resonant frequency (1MHz) so when the transistor is operating current is allowed to flow through the RC circuit. At resonant frequency the transistor is said to be switched on  i.e 0.7V entering the base and this in turn makes it behave as an amplifier once ac signal ia added to it.  R2 and C1 in series act as a high pass filter along with C2 and RL filter out frequencies below our desired range. while  Re and Ce act as a low pass filter and cut off high frequencies hence giving us the range of our bandwidth. Capacitors C1 and C2 are also called coupling capacitors as they filter out the DC voltage in our circuit.

     

Intro

Common emitter amplifier circuit

The amplifier we are designing should operate at 1MHz, we have been advised to begin by Professor Steve Taylor, who is the project supervisor, to begin by designing a 100kHz common emitter amplifier, then increase the specification to 1MHz. The purpose of the amplifier designed is to operate an ion trap control which will be used in public places like airports to check for illegal substances. The design we used is similar to a common emitter amplifier above  but has the emitter capacitance omitted as we designed the amplifier to have a large bandwidth as we were given no limit.