EC Fundamentals - Operational Amplifiers

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EC basics


A firmware engineer, in addition to software coding skills, also needs basic hardware knowledge.

This is because firmware engineers often collaborate with hardware engineers to troubleshoot and

resolve problems; therefore, hardware knowledge is one of the essential skills for a firmware engineer.

This article will begin by introducing commonly used operational amplifiers to build a solid foundation

for a firmware engineer.


operational amplifier


An active element with two inputs can perform functions such as addition, subtraction, comparison,

differentiation, and integration by making some changes to the input or gain elements.


  • Electrical characteristics


  • Input resistance [Rin] – Ideally, infinite.

  • Input capacitance [Cin] – Ideal value 0

  • Input offset voltage [Vio] – The voltage difference that must be applied across the

                        input terminals to obtain zero output voltage. Ideally, it should be 0.

  • Input offset current [Iio] - The current difference that must be applied across the

                        input terminals to achieve zero output voltage. Ideally, it should be 0.

  • Power Supply Voltage Rejection Ratio (PSRR) – The ratio of the input offset voltage

                        variable to the power supply voltage variable.

  • Common-mode rejection ratio (CMRR) – The ratio of common-mode voltage to

                        common-mode error voltage; ideally, the value is infinitely large. This represents the
                        noise rejection capability.


  • Inverting amplifier


Because the output signal and the input signal source are out of phase, it is called an inverting amplifier.

Since Vi=0 and Ii=0 for the OPA, the current [I] flowing through the input resistor [Ri] is also equal to

the current [I] flowing through the feedback resistor [Rf].


  • Non-inverting amplifier


Because the signal is input from the non-inverting input terminal, and the output signal is in phase with

the input signal, it is called a non-inverting amplifier.Since Vi=0 and Ii=0 for the OPA, the current [I]

flowing through the input resistor [Ri] is also equal to the current [I] flowing through the feedback

resistor [Rf].


  • Comparator


  • Comparator Examples

  • If we disregard the state of BL/C# and assume PR75 is open, then Vin = 7.33V

                    is required to achieve Vo = 0V.

    • Vin > 7.33V, Vo = +VDD

    • Vin < 7.33V , Vo = -VDD = 0V

    • Vin = 7.33V , Vo = 0V



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