3 Summary

In summary, there are five good reasons why a 3-6db matching pad is useful when sandwiched between the balun outputs and ADC’s analog inputs.

1. Facilitating support of the customer EVM across a broad range of application bandwidths.
2. Providing an efficient method to use the full bandwidth capabilities of an ADC.
3. Makes for a stiff balun output impedance.
4. Makes for a solid ADC input impedance.
5. Mitigates passband ripple and standing waves.

While this can seem counter intuitive that a lossy balun or interface network is not always attainable, particularly when designers do not see any improvement in noise figure (NF) calculations or signal chain lineup analysis, the value cannot be understated. For passive interface networks, this has proven to be beneficial and effective and is almost always required for wideband or high frequency applications exceeding the 3-4GHz range.