I am confused about the definitions of these amplifiers. It seems LNA is used for RF frequency band but I also see people using INA's for receiver.

  1. Why LNA's need careful impedance matching but INAs are not?
  2. Can LNA's be used for low frequency (below 100Hz) high impedance(10kΩ) sensors?
  • \$\begingroup\$ Good to know LNA = Low Noise Amplifier. \$\endgroup\$ – jippie Jun 20 '15 at 6:45

Preamplifier is a role rather than specific topology. It's the first amplification stage, which sits as close as practical to a sensing element (or an antenna). The goal is to amplify the signal before sending it over the cable to the main amplifier. If an unamplified signal straight from the sensing element is sent over the cable, it may get degraded by the EMI picked up by the cable. If the signal is amplified before the cable, then the signal to noise ratio will be higher.

re: 2
InAmps are good for things like sensor signal conditioning. But InAmp performance degrades with frequency. InAmps are typically used with signals below 100kHz. If you haven't seen it already, here's the definitive source of information about InAmps: A Designer's Guide to Instrumentation Amplifiers (3rd Edition) by Analog Devices

re: 4
Signals with frequencies under 100Hz is a domain of OpAmps and InAmps. There are techniques for working with high impedance sensors (perhaps, this chapter may help).

  • \$\begingroup\$ Thanks for your detailed answer. I did go through Designer's Guide to Instrumentation Amplifiers (3rd Edition) by Analog Devices. It did not contain a lot about noise analysis. Why low frequency signal form high impedance sensors doesn't need matching? And why instrumentation amplifiers can't be low noise INA? \$\endgroup\$ – tendo Jun 20 '15 at 18:19

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