LTC6421IUDC-20#PBF

Overview

The LTC6421IUDC-20#PBF is a dual matched 1.3GHz differential amplifier and ADC driver from Analog Devices Inc., housed in a 20-lead 3mm × 4mm QFN package. It features a fixed gain of 20dB (10V/V) with a 200Ω differential input impedance. The device operates on a single supply voltage ranging from 2.85V to 3.5V, drawing 40mA per amplifier. It supports an output common mode voltage adjustable between 1V and 1.6V via external pins. Key performance metrics include a noise figure of 6.2dB at 100MHz, equivalent OIP3 of 42dBm, and channel separation of 80dB.

Feature Summary

• Dual matched amplifiers with tight gain matching of ±0.1dB and phase matching of ±0.2° at 100MHz.
• Integrated output common mode biasing allows direct driving of ADCs without transformers or AC-coupling capacitors.
• Rail-to-rail output swing capability ensures maximum dynamic range for high-speed data conversion applications.
• Low power consumption design with 40mA supply current per amplifier and dedicated shutdown functionality.

Applications

• Differential ADC Driver
• Single Ended to Differential Conversion
• IF Sampling (Diversity) Receivers
• Broadband I/Q Amplifiers
• Satellite Communications

Procurement Notes

Verify the specific suffix '#PBF' indicates lead-free finish and tube packaging when ordering. Confirm the 'I' grade designation matches the required -40°C to 85°C operating temperature range for your application environment. Ensure the 20-lead QFN footprint dimensions align with your PCB layout constraints before finalizing procurement.

Selection Notes

Select this component for applications requiring precise channel-to-channel matching and high linearity up to 140MHz. The fixed 20dB gain suits systems needing significant signal amplification without external feedback resistors. Consider the 200Ω input impedance for source matching requirements. Evaluate the 1.3GHz bandwidth against your highest frequency signal components to ensure adequate headroom.

Part Context

This part belongs to the LTC6421 family of dual matched differential amplifiers. It shares architectural similarities with the LTC6420 but offers higher gain. It complements other members like the LTC6400 series which provide lower distortion options. The device is designed to interface directly with high-speed analog-to-digital converters commonly used in communication systems.

Replacement Considerations

LTC6421CUDC-20#PBF serves as a commercial grade alternative with a 0°C to 70°C temperature range. For single-channel implementations, consider the LTC6401-20. Lower gain variants such as the LTC6421-8 or LTC6421-14 are available if different amplification factors are required.

FAQ

How is the output common mode voltage controlled?

The output common mode voltage is set independently using the VOCMA and VOCMB pins. These pins accept an external DC bias voltage within the 1V to 1.6V range, allowing direct interfacing with ADC common mode inputs.

What is the differential input impedance?

The differential input impedance is nominally 200Ω. This internal impedance simplifies matching networks for sources with similar impedance characteristics or allows for specific termination strategies for 50Ω sources.

Can the device operate with AC-coupled inputs?

Yes, the LTC6421-20 supports both DC-coupled and AC-coupled operation. When AC-coupled, the input common mode voltage is automatically biased close to the VOCM setting, eliminating the need for additional bias circuitry.