The first thing students learn about an operational amplifier is that its gain is incredibly high. Now if a feedback resistor is connected between the negative input terminal and the output terminal, an extremely high current is reflected, which goes through the feedback resistor. This simple design is called the transimpedance amplifier and is used much more commonly than you’d think.
While you might think the design of a transimpedance amplifier is relatively simple, there are a lot of different factors that you need to carefully consider. So, if you’re designing a transimpedance amplifier, keep these factors in mind.
DO – Stabilize Your Design:
Because of the incredibly high gain of a transimpedance amplifier, you need to stabilize your design. The easiest way of doing so is by analyzing the Bode plot of the design. For those of you who don’t know, a bode plot depicts the gain and the phase response of a linear time invariant system for a bunch of different frequencies.
To ensure that your TIA performs reliably, make sure to minimize any wild oscillations in the Bode plot. This can be achieved in a variety of different ways. The simplest method of removing these oscillations is to separate each circuit in your TIA design into amplifiers with an open loop gain as this makes analysis and component selection much easier!
DON’T – Forget To Compensate:
Another way to stabilize your design is by compensation. The most efficient way of providing phase compensation is by using a bypass capacitor. A simple capacitor can be connected in parallel with the feedback resistor to guarantee sufficient compensation for the phase. If you want to calculate the capacitance of the bypass capacitor, use this simple equation
The bypass capacitor essentially inserts a zero in the feedback factor, which, in turn, modifies its Bode plot. The new zero provides sufficient compensation for the phase shift and stabilizes your design.
However, it’s important that you don’t go overboard with the compensation as it can have major ramifications on the usefulness of the TIA. If you use a bypass capacitor with a higher capacitance, you will effectively reduce the bandwidth of the TIA, which will make it unsuitable for high frequency applications!
DO – Calculate the TIA’s Design Frequencies:
To calculate the design frequency of the Transimpedance Amplifier, you need to refer back to the bode plot of the TIA. As the bode plot shows the response of the TIA when exposed to different frequencies and also gives information about its close loop noise gain, you can use this information to determine the amplifier’s design frequencies.
If the lowest frequency of the amplifier is denoted by fAOL (which consequently represents its dominant pole), and GBWP represents the amplifier’s Gain Bandwidth Product, you can use the following relation to determine the fAOL;
Where, Aol is the amplifier’s open loop gain.
We believe that if you follow these simple rules, you can easily find out the specifications of your required transimpedance amplifier. Furthermore, you can use these relations to determine the design frequencies of the transimpedance amplifier which will help you come up with a design that’s not just operational but is reliable as well!
Once you have finished your calculations and know exactly what you want from the market, head on over to our online store.
We have a vast collection of transimpedance amplifiers which will make it easier for you to find one that best fits your need. All our products are rigorously tested for quality before they’re advertised so you know exactly what you’re paying for!
We also have an incredible library of other useful electrical components such as variable delay lines, phase shifters, and much more!