Bode diagrams and 2-port networks

Abstract

OFTEN WE want to know how a circuit will behave as the frequency changes, apart from any transient response, particularly with devices such as filters. (To some extent any circuit containing reactive components acts as a filter, that is it attenuates more at some frequencies than at others.) Any network may be so arranged as to have a pair of input terminals (the input port) and another pair for output (the output port) as in Figure 5.1 a. The ratio of output voltage to input voltage is written

$$$$

(5.1)

where A_v (= |V_o/V_in|) is the amplitude response and 4) the phase response of the circuit. Conventionally these are displayed together on a Bode diagram¹, which is a plot of voltage gain (in dB, or 20log₁₀ A_V and phase against log frequency.