An Introduction to the Design of Filters and Sinusoidal Oscillators

After making a review of existing first-year laboratory work at Manchester Metropolitan University dealing with active filters, the authors describe an alternative set of first-year experiments which cover the three first-order filters whose transfer functions are controlled by a single time constant (first-order STC filters), namely, lowpass, highpass and allpass. The allpass filter can be regarded as an elementary parallel-path circuit with zero-order feedforward and this technique is extended to develop lowpass-to-highpass and highpass-to-lowpass converters which as well as allpass filters can be employed in the design of sinusoidal oscillators whose oscillation frequency can be adjusted using two similar grounded elements. Two approaches to the design of one such oscillator are given and experimental results are provided.