Bob - you asked "For example, if an op amp has a bandwidth of 10 MHz, what happens when its fed a 100 MHz signal?"
Most likely RF rectification - conversion to DC or low frequency noise if 100MHz (or higher frequency) is modulated. It is caused by different response for positive and negative slope and is present in practically all OP-Amps or Instrumentation Amps.
OP-amp should always have RC filter if front of it to prevent it. Common mode rejection of differential (balanced) connection works at lower frequency range while normal mode rejection (filter) prevents RF rectification.
Most likely RF rectification - conversion to DC or low frequency noise if 100MHz (or higher frequency) is modulated. It is caused by different response for positive and negative slope and is present in practically all OP-Amps or Instrumentation Amps.
OP-amp should always have RC filter if front of it to prevent it. Common mode rejection of differential (balanced) connection works at lower frequency range while normal mode rejection (filter) prevents RF rectification.