ENGINEERING KNOWLEDGE CENTER

What is a Current Amplifier?

A Current Amplifier converts a very small electrical current into a measurable voltage signal while maintaining high accuracy and low noise.

Measurement Principle

A current amplifier converts an extremely small input current into a measurable output voltage. This technique is known as transimpedance amplification and is widely used for photodiodes, PMTs, APDs, ion detectors and other current-output sensors.

Instead of measuring current directly, the amplifier uses a precision feedback resistor to generate a proportional output voltage while maintaining excellent linearity, low noise and high bandwidth.

Basic Equation

Vout = Iin × Gain

Output voltage is directly proportional to the input current and the selected transimpedance gain.

Example:
Input Current = 10 nA
Gain = 10⁸ V/A
Output Voltage = 1 V

Why do we need a Current Amplifier?

Many scientific sensors such as photodiodes generate only picoampere (pA) or nanoampere (nA) level currents.

These currents are too small to measure directly with an oscilloscope. Therefore a low-noise current amplifier converts the current into a voltage that can be accurately measured.

Basic Principle


Photodiode
     │
     ▼
Current (nA)
     │
     ▼
Current Amplifier
     │
     ▼
Voltage (V)
     │
     ▼
Oscilloscope

Gain Selection Guide

Select a gain that produces a measurable output voltage without saturating the amplifier. A practical starting target is often between approximately 0.1 V and 5 V.

1 pA10¹¹ V/A0.1 V

10 pA10¹⁰ V/A0.1 V

100 pA10⁹ V/A0.1 V

1 nA10⁸ V/A0.1 V

10 nA10⁷ V/A0.1 V

100 nA10⁶ V/A0.1 V

1 µA10⁵ V/A0.1 V

This table is a starting guide. The final gain must also consider peak current, detector offset, required bandwidth, noise and output saturation.

Current Amplifier Calculator

Photodiode Current (nA)

Gain (V/A)

Result

1.000 V

Recommendation: Excellent operating range.