3.7: Cascaded Op Amps
Operational amplifiers (op-amps) are versatile electronic components that can be interconnected in a cascade - one after another in a linear sequence. This cascading is possible due to their infinite input resistance and zero output resistance, allowing them to maintain their input-output relationships even when connected in series.
In a cascaded system, each op-amp is referred to as a stage. The output of one stage drives the input of the subsequent stage. As the input signal passes through each stage, it is amplified by the gain of that stage. The resulting overall gain of the cascaded system is equal to the product of the gains of each stage.
This cascading approach offers several advantages. By distributing the total gain among multiple stages, each stage has less gain than if a single op-amp was used. However, since the gain-bandwidth product remains constant for each op-amp, reducing the gain at each stage effectively increases the bandwidth at that stage. This leads to an overall increase in the bandwidth of the cascaded system.
Cascaded op-amps find extensive use in tuned RF amplifiers found within television circuits. These cascaded amplifiers amplify weak signals and improve impedance matching at the input and output, delivering high-quality audio and video signals to the viewers.
However, designing a cascaded op-amp circuit requires careful consideration. The individual gains must be set such that they do not saturate the signal in the various stages of the cascade. Signal saturation can distort the output, leading to poor performance.
