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gm-c filter tuning operating over subthreshold

mkza1002

 i am working on gm-c filter to obtain the linear charactarstics of current and voltage relationships , but due to not having pure sinusoidal signal in analog library my o/p provides different currents w.r.t input signal.hence please advice and help me out.how can i get up pure sinusoidal i/p. right now the sinusoidal input has a cone shape around the highest amplitude region where it should be a smooth curve.

  • You didn't mention the simulator (I assume spectre), but in practice this is the same for all circuit simulators. I assume you're using either vsin or vsource (with type being sine) from analogLib.

    These are producing a pure sinusoidal signal. However, when plotting waveforms from a circuit simulator, it's only the points that are valid not the lines between the points (these are a drawing aid to help humans visualise things). The points themselves will be on the pure sinusoidal signal. The simulator is still accurate, but circuit simulators adapt the timestep to ensure a reasonable balance between accurately following signals and running quickly - the point is that the circuit simulator will solve the circuit equations according the tolerance/accuracy settings, and take tighter timesteps if needed.

    So your problem is not due to inaccuracy of the sinusoidal sources in the simulator. It's not actually clear what your problem is, but this isn't it...

    Regards,

    Andrew.

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