A novel SFG structure for C-T high-pass filters

A signal flow graph (SFG) structure for simulating passive high-pass ladder filters, called the incremental integration structure, is proposed. The structure requires the use of integrators with nonintegrating inputs, and an implementation based on the MOSFET-C technique is discussed. The incremental integration structure is compared to the leapfrog and direct SFG simulation structures. Leapfrog high-pass filters are relatively simple and show good noise properties, but they are based on differentiators and thus stability problems exist. The direct SFG simulation method is based on integrators and has good stability properties, but it leads to a relatively high circuit complexity and a high noise level. However, the incremental integration structure inherits the low-noise properties of the leapfrog structure and the good stability of the direct SFG simulation method. A sixth-order elliptic high-pass filter chip with a passband frequency of 3.0 kHz has been manufactured, and measurements support the validity of the approach