How to achieve high impedance input on opamp?
An approach to high input impedance buffering with an op-amp is to create a non-inverting unity gain buffer, using a very high input impedance op-amp, such as the Intersil CA3140 (1.5 Tera Ohms), or the Texas Instruments OPA2107 (10 Tera Ohms), both of which have a Gain Bandwidth Product of 4.5 MHz.
Can you use an attenuator in front of an amplifier?
Well not necessarily; as mentioned previously a passive attenuator in front of a noninverting amplifier would work and provide a noninverted output. You could also use a differential amplifier or a difference amplifier; both use the gain equation G = RF/RG.
What is the input impedance of a unity gain buffer?
In a non-inverting unity gain buffer configuration, the input impedance of the buffer is the input impedance of the op-amp itself, and resistance noise is minimized / none. One other factor, though, is the input capacitance of these op-amps, 4 pF in the case of both these example op-amps.
What is the noise gain of an amplifier?
Remember that it is the noise gain, not the signal gain that determines amplifier stability. The noise gain, which is the same for both inverting and noninverting amplifier configurations, is equal to the noninverting gain equation. For example if an inverting amplifier has a signal gain of -0.5, it still has a noise gain of 1.5.
What does a cap do to an op-amp?
The cap would reduce Unity-Gain Bandwidth of your Op-Amp and hence corrects your phase margin. Second, you can reduce gain of feedback loop (the feedback here is the wire from emitter of Q1 to node 13).
Can you limit the bandwidth of the loop gain?
You cannot change or “limit” the frequency response of the opamp unit – however, you can limit the bandwidth of the loop gain (which is responsible for oscillatory behaviour). This can be done, for example, with a R-C series combination BETWEEN both opamp inputs (nodes 12 and 13).