Transimpedance Amplifier

安圣基

Transimpedance Amplifier [Copy link]

Does anyone know why a TIA is used for I/V conversion in a photodetection circuit, rather than a resistor + voltage follower? What are the advantages of choosing a transimpedance amplifier?

chunyang

Because the equivalent impedance of the photosensitive tube is high and the output is current type, a transimpedance amplifier can be used to convert the current input into a voltage output, while also having a high noise suppression rate.

If voltage input is used, the output of the photosensitive tube must first be converted into a voltage signal through a resistor. Since the photocurrent is very small, a higher resistance value is required, which places higher requirements on the input impedance of the op amp. High-impedance loops are more sensitive to electromagnetic induction noise.

As for the voltage follower, since the gain is 1, the signal amplitude obtained by the subsequent circuit is still very low and generally cannot meet the requirements. Since amplification is required, a follower will naturally not be used.

maychang

What are the advantages of choosing a transimpedance amplifier?

There is no "advantage" to speak of, except that the transimpedance amplifier is more suitable than the voltage amplifier for photoelectric detection, a device with very high output resistance.

呜呼哀哉

There is little information available on this structure of op amp. Do you have any relevant information? I also encountered a similar problem and did not solve it.

led2015

Using TIA as a means of I/V conversion can improve the circuit's noise performance, bandwidth, and linearity.

820148214

If you don't pursue performance, you can use ordinary op amps, but using transimpedance amplifiers is easier to improve the various indicators of the circuit.

安圣基

chunyang posted on 2023-4-18 15:04 Because the equivalent impedance of the photosensitive tube is relatively high and the output is current type, a transimpedance amplifier can be used to convert the current input into a voltage output, and at the same time, the noise suppression rate is relatively high...

Thanks for your responses.

Why does TIA have a high noise suppression rate? What is the source of this noise?

chunyang

An Shengji posted on 2023-4-23 09:06 Thank you for your reply. Why does TIA have a higher noise suppression rate? What is the source of this noise?

The noise here mainly refers to the electromagnetic noise in the sensing space. If a voltage input amplifier is used, a current-to-voltage conversion resistor with a higher resistance must be used when the photocurrent is very weak. In this way, the loop formed by the high-value resistor, the phototube, and the op amp input naturally presents a high impedance characteristic. The electromagnetic interference in the space will also induce a higher noise voltage in the high-impedance loop, so the signal-to-noise ratio is insufficient.

The transimpedance amplifier has a current input and voltage output structure, and its equivalent input impedance is much lower than that of a voltage input amplifier (close to 0), so the induced voltage of spatial electromagnetic interference will be much lower. In addition, the same is true for the thermal noise of the device itself.

It is easier to understand with an ideal op amp. For a non-inverting proportional amplifier, its input impedance is infinite. For an inverting proportional amplifier, its input impedance is the resistor connected in series with the input terminal. For a transimpedance amplifier, its input impedance is 0. Based on the input impedance, we can draw a conclusion using Ohm's law.

hjl2832

I think the main reason is that the input impedance of the transimpedance amplifier is higher, and it is more suitable for components that require high input impedance, such as photosensitive tubes. If you choose a common op amp with high impedance input and low IB current, it should be able to achieve the same effect.

MrCU204

Photosensitive tubes are photoconductive and photoelectric tubes are photovoltaic, but their output is pitifully small.

The advantage of current control is that it is straightforward. The photosensitive tube can be treated as a wire without conversion. The circuit is simple, the input impedance is low, and interference is powerless to cause harm. The output parameter is voltage, which depends on Vcc, and the gain can be very high.