Why Matching Matters in Dual JFETs: Improving Precision Differential Amplifier Performance

When designing a precision differential amplifier, low noise is only part of the equation.

The two input transistors must behave as similarly as possible. Even small differences in electrical characteristics can introduce input offset voltage, reduce common-mode rejection (CMRR), increase temperature drift, and ultimately limit the accuracy of the entire circuit.

That's why device matching is so important.

Rather than pairing two individual transistors, many engineers choose a monolithic dual JFET, where both devices are fabricated on the same piece of silicon. Sharing the same die allows the transistors to track each other much more closely—electrically and thermally—resulting in more stable, predictable performance over temperature and time.

The LSK389 was developed for exactly these types of applications. Its monolithic dual construction combines ultra-low noise with tightly matched electrical characteristics, making it well suited for differential input stages used in instrumentation, medical electronics, scientific measurement equipment, sensor interfaces, and professional audio.

Key Benefits of the LSK389

• Monolithic dual JFET construction

• Ultra-low noise (1.6 nV/√Hz typical @ 1 kHz)

• Tight gate-to-source voltage matching (15 mV max)

• Excellent thermal tracking

• Optimized for precision differential amplifier input stages

In precision analog design, matching isn't simply another specification—it directly affects stability, accuracy, and long-term performance.

Linear Systems Learning Series: Helping engineers better understand precision analog design.