Bilinear transform
The bilinear transform (also known as Tustin's method, after Arnold Tustin) is used in digital signal processing and discrete-time control theory to transform continuous-time system representations to discrete-time and vice versa. The bilinear transform is a special case of a conformal mapping (namely, a Möbius transformation), often used for converting a transfer function H a ( s ) {\displaystyle H_{a}(s)} of a linear, time-invariant (LTI) filter in the continuous-time domain (often named an analog filter) to a transfer function H d ( z ) {\displaystyle H_{d}(z)} of a linear, shift-invariant filter in the discrete-time domain (often named a digital filter although there are analog filters constructed with switched capacitors that are discrete-time filters).