1st Lab

We received the electronic components we ordered before Christmas holiday. There are 2 kinds of transistors. Unfortunately, they are not exactly required by the circuit. Besides, transistors only are not enough to build the circuit.

We discussed together and decided to order new components which are exactly what the circuit need. We printed a new component list, and search the Internet to find out more information about every component we need. We also went to the technicians to check whether they have the resistors and capacitors we need. Finally, we need to order 3 kinds of transistors from the website. And we handed in the final component list to the technicians, hoping the components could arrive before the next lab.

We tried to design our own circuit this afternoon.  We went to the computer room to search further about the project. What's more, we reviewed some knowledge from the first year to learn more about the important component: operational amplifier.

An operational amplifier has two differential inputs but usually only a single-ended output and should be connected to a couple of opposite DC power supply. It is a high-gain electronic voltage amplifier since the output from an op-amp is hundreds of thousands of times higher than the voltage difference between its input terminals. Most op-amp are Integrated Circuit (IC) chips. What we chose is UA741CN.

The power supply voltage Vcc and VEE power the operational amplifier and in general define the output voltage range of the amplifier.

In this project, in order to invert the original AC signal, we need to use a negative feedback to the fundamental op-amp configurations to constitute a inverting amplifier.

The feedback circuit provides a fraction of the output signal, βVo, which is subtracted from the input source signal, Vs. The resulting signal, Vi, which is also called the error signal, is the input to the amplifier which in turn produces the output signal Vo = AVi. The gain Vo/Vs of the inverting amplifier is given by

In the inverting amplifier, output voltage that is fed back into the inverting input by the feedback resistor network and the voltage gain can be calculated as 

The negative sign for the gain indicates that the polarity of Vo is opposite to the polarity of Vin.