3 Amplifiers vs. Baluns: The Advantages

On the active side, you can use an amplifier to preserve the DC levels, also known as the DC bin. This type of amplifier/ADC interface in the signal chain is often referred to as DC coupling. Therefore, these DC levels hold some important information in a particular application.

Amplifiers can also maintain better isolation in previous stages in the RF signal-chain lineup, which matters when using unbuffered converters, or if standing waves are evident when the front-end match is not quite right within the frequency band relevant to the application.

Although amplifiers inherently provide +6dB of gain or more, that gain is independent of the output impedance. The amplifier’s bandwidth do not suffer or drop when this comes to subtle fluctuations in impedance across the frequency band of interest. Because the amplifier is more autonomous with gain vs. output impedance, amplifiers typically enjoy a more ripple-free passband.

On the passive side, baluns cannot pass DC levels, and transformers are inherently flux coupled devices, which make them good AC couplers. Or, DC blockers. For inherently AC-coupled RF signal-chain lineups, baluns are a great choice. Baluns are naturally passive and need no power supply nor supporting circuitry such as decoupling capacitors or ferrite beads for power. And because baluns need no power supply, baluns are essentially noiseless.

Surface mount technology (SMT) baluns is common in providing upwards of 10GHz and even 20GHz of bandwidth. If you opt for a modular type balun—for use in a lab setting or high-end instrumentation—those baluns are hitting upward of 80GHz at the time of this writing. If the bandwidth requirement for the application is paramount and you need more than 5GHz, the balun seems to outshine the amplifier.