Low-Distortion, Low-Noise Composite Operational Amplifier

Groner S, Polak M. Low-Distortion, Low-Noise Composite Operational Amplifier. J Audio Eng Soc. 2017;65(5):402-407. doi:10.17743/jaes.2017.0008

@article{Groner2017_18733,
  author = {Groner, Samuel and Polak, Martin},
  title = {{Low-Distortion, Low-Noise Composite Operational Amplifier}},
  journal = {Journal of the Audio Engineering Society},
  volume = {65},
  number = {5},
  pages = {402--407},
  year = {2017},
  month = may,
  publisher = {Audio Engineering Society},
  doi = {10.17743/jaes.2017.0008},
  url = {https://doi.org/10.17743/jaes.2017.0008}
}

TY  - JOUR
TI  - Low-Distortion, Low-Noise Composite Operational Amplifier
AU  - Groner, Samuel
AU  - Polak, Martin
T2  - Journal of the Audio Engineering Society
J2  - J. Audio Eng. Soc.
VL  - 65
IS  - 5
SP  - 402
EP  - 407
PY  - 2017
DA  - 2017/05/06
DO  - 10.17743/jaes.2017.0008
UR  - https://doi.org/10.17743/jaes.2017.0008
PB  - Audio Engineering Society
LA  - en
AB  - In state-of-the-art implementations of instrument devices, a single amplifier stage may be required to provide a THD figure of better than -140 dB for a 5V RMS, 20 kHz signal in order to support a total instrument dynamic range of 120 dB in an 80 kHz measurement bandwidth. Currently it is not possible to achieve this performance level using available commercial monolithic operational amplifiers in a standard configuration. A proposed design approach achieves this goal. A unity gain stable composite operational amplifier is presented that consists of a cascade of two operational amplifiers, an intermediate compensation network and a frequency-selective feedback network for the second amplifier. This configuration achieves very high open-loop gain (100 dB at 100 kHz) and thus shows exceptionally good distortion characteristics. Furthermore, the noise characteristics of the first operational amplifier are preserved. The open-loop response is designed for conditional stability, such that a very-large-gain-bandwidth product at signal frequencies can be achieved. A numerical optimization procedure is then introduced to derive the frequency compensation, based on specific stability criteria. Measurement results confirm the predicted high-gain-bandwidth product (10 GHz at 100 kHz) and excellent distortion performance (-180 dB). Applications for the new composite operational amplifier include audio frequency distortion measurement equipment.
ER  -