Electronics is Fun

In the first part of the series we made an introduction about the noise and how we can categorize them into device noise, emitted noise, and conducted noise. We first discussed about the most common noise, the Johnson noise coming from a resistor . This noise is also a white noise, due to the fact that it is present at all frequencies. This noise is produced whether or not a resistor is connected in a circuit. When a resistor is connected to a circuit, say to an amplifier, this resistor will be a source of noise to the circuit. Let's take an inverting operational amplifier as an example that has two resistors connected to it, one at the input and the other one as feedback. The noise due to the resistors can be modeled as noise sources in series with the resistors. Figure 1 Resistor Noise In order to appreciate its effect in the circuit, we must be able to understand how these noise affect the behavior and output of the amplifier. Modeling the noise sources as in the f...

I am back from a little hiatus. I've been meaning to write something about noise in the circuits, because I know it's one of the least understood topics in electronics. It's something that one can easily attribute to when something goes odd in the circuit, yet so few have the courage to delve into it. In audio applications, it's easy to describe what noise is. We know if the music is clear and pure, it is free of noise. Anything that is unwanted we can call noise, well, in a broad sense of the word. Noise comes in different forms and from different sources, but in the hope of making some order out of chaos we can attempt to categorize them in the following: 1. Device Noise - noise coming from active and passive devices 2. Emitted Noise - those coming from power lines, motors, radio trasmission, etc. 3. Conducted Noise - those that are already in the circuit, either from the device or transmitted into Electronics components are indeed sources of noise in the ci...

by DarwinT Well I've been taught in school only one thing about the bandwidth of an op amp, or perhaps it just didn't register enough in my brain that there's another kind of bandwidth, and all of a sudden I hear this large signal bandwidth, or sometimes referred to as the full-power bandwidth, about op amps. At first I thought that this "large signal bandwidth" thing should be pretty obvious and a no-brainer, until I got confused some and I realize it can't be ignored anymore. That I already know, and I wanted to know more about it. How come nobody explained this thing to me! When you look at an op amp's datasheet (e.g. ADA4895-1 ), the manufacturer often publish the bandwidth on the front page, otherwise it can always be found in the collections of plots inside. It's basically the unity gain frequency of the open loop gain of the amplifier. What is not so obvious is that this doesn't apply to all level of signals you intend to use your amp...

Basic Integrator If you strap a capacitor around an op-amp as a feedback in an inverting configuration, instead of a resistor, you wind up with an interesting basic circuit called an integrator. The name comes from the fact that the circuit basically does a mathematically integrating function, expressed in the output transfer function. This circuit can be very confusing to many. I think the best way to understand it is from a practical point of view, by way of analogies and equivalent circuits. And once you are able to get a mastery of its functions and behaviors, there’s a lot of interesting opportunities where the basic circuit can be useful. Current Flow and Output Equation The output is a derivation applying KCL (Kirchoff’s Current Law) at the amplifier’s summing node, and the op-amp’s ideal assumptions namely that the positive and negative terminal are at the same potential, and no input bias current flows. The voltage input creates a current in the resi...

School has probably taught most of us that an op amp is a black box with a set of ideal and non-ideal characteristics. We often easily derive the output equations using ideal assumptions, which includes infinite open loop gain, zero input offset, zero input bias currents, and zero output impedance, etc. But in order to fully appreciate its capabilities and limitations, it helps to know why they came about in the first place. And it is primarily because its use with negative feedback. It always helps me to think that op-amp is basically a device that takes a differential input and amplifies it with its large open loop gain. One can't go wrong with the inputs that are always labeled with positive and negative. A small differential input would drive the output large positive or negative depending on the polarity of the differential input. Negative feedback is what makes the op amp very useful in applications such as amplifiers and signal conditioning circuits. The follow...

Our aim here is to discuss the very important concepts and give intuitive explanations of the subjects. We'll start with the resistor which is the most straightforward, then with the less understood and often misunderstood concepts of capacitance and inductance. We will discuss the R-C and R-L circuits as well. These along with Ohm's Law, Kirchoff's Voltage Law (KVL) and Kirchoff's Current Law (KCL) are the very foundations of understanding the complete behaviors of practically any circuit one might encounter. Resistance It is a general term that refers to the opposition to the free flow of current in a circuit. More accurately, it refers or applies to DC (direct current). Resistance doesn't apply only to resistors but also to a host of other components in the circuit. For example, a copper trace has a resistance according to its dimensions, as well as the leads of he components.When a current flows through a resistor a potential difference is generated acr...