1–2 Operation
1.1 Overview
The SIM965 Analog Filter is a continuous-time, digitally-programmable
filter with fully analog signal paths. By using a modified state-
variable circuit design, the SIM965 provides a variety of programmed
filter configurations. From the front panel, the user can select a But-
terworth filter, for maximum passband gain flatness, or a Bessel
filter, for minimum pulse overshoot and constand time delay in the
passband. The user can also select either a low-pass or high-pass
filter, and change the order of the filter between 2nd, 4th, 6th, or 8th
order, corresponding to 12, 24, 36 or 48 dB/octave roll-offin the stop
band.
For any filter configuration, a single continuous parameter, the “cut-
offfrequency,” fccan be set with 3-digit resolution (and ±1 % ac-
curacy) in the range of 1 Hz to 500 kHz. For Butterworth filters, fc
corresponds to the frequency at which the filter response is −3 dB. For
Bessel filters, fcis determined so that the far-stop-band attenuation
slope asymptotically approaches that of the Butterworth filter.
Figure 1.1: The SIM965 front and rear panels.
SIM965 Bessel & Butterworth Filter
