84 Chapter 5 OPA627 spectral density (nV/ Hz ) 1000 Spectral density (nV/rt-Hz) 100 Measured noise, with scale adjusted and aberrant data points removed. 10 Average noise 1 0.1 1 10 100 1000 Frequency (Hz) 10,000 100,000 Figure 5.33: Spectral density measured results Input voltage noise spectral density 1K OPA627 Voltage noise (nV/Hz) 100 Data sheet noise 10 Measured noise 1 1 10 100 1k 10 k 100 k 1M 10 M Frequency (Hz) Figure 5.34: Comparison of the measured spectral density to data sheet 5.10 Measure Low Frequency Noise for the OPA227 Many data sheets have a specification for the peak-to-peak noise from 0.1 Hz to 10 Hz. This effectively gives an idea of the op-amp's low frequency (i.e., 1/f noise). In some cases, this is given as an oscilloscope waveform. In other cases, this is listed in the specification table. Figure 5.35 shows one effective way of measuring the 0.1­10 Hz noise. This circuit