john guy @ edn.com writes:
Intrinsically capacitive transducers and other high-impedance signal sources usually require ac coupling and a buffer amplifier to condition the signal for further processing. Buffers take many forms, but most of them compromise signal quality through the use of external resistors that provide a dc path for the input bias current. Recent improvements in op-amp technology allow ac-coupled inputs without the need for bias resistors.
Amplifier requires no dc bias – [Link]