Stanford Research Systems SR865A, Operation Manual

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Appendix A Advanced Filters 157
SR865A DSP Lock-in Amplifier
The BlazeX output is always an RC filter (1 to 4 poles) regardless of the front panel
Advanced Filter setting. This is because the BlazeX output is intended for feedback
applications that require low latency.
Summary of Filter Characteristics
The chart below summarizes the speed of the different filters. (also see Step Response
graphs on the following pages).
The chart below summarizes the noise bandwidth of the different filters. Note that for a
single stage, all 3 filters are designed with the same noise bandwidth.
Equivalent Noise Bandwidth (fraction of f
c
=( 2π ×time constant)
− 1
)
Stages RC Gaussian Linear Phase
1 1.6 1.6 1.6
2 0.79 1.1 0.93
3 0.59 0.94 0.83
4 0.5 0.81 0.78
Time to settle to within 1% of final value (in time constants)
Stages RC Gaussian Linear Phase
1 4.6 2.3 4.6
2 6.6 4.0 4.4
3 8.4 5.6 4.8
4 10.0 7.1 5.4