JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech II ELECTRONIC CIRCUITS Previous Question Paper (August/September - 2022 - R16)

The h-parameters (hybrid parameters) of a transistor are defined based on the relationship between input/output voltages and currents in a two-port network. For a common-emitter configuration, the equations are:

Where h_ie is input impedance, h_re is reverse voltage transfer ratio, h_fe is forward current gain, and h_oe is output admittance. The benefits of using h-parameters include:

• They are real numbers at audio frequencies, simplifying circuit calculations.
• They are easily measured in a laboratory setting using standard AC meters.
• They provide a standard method for characterizing transistors regardless of internal construction.
• They are convenient for circuit analysis as they use a mix of impedance and admittance parameters, which match the input and output characteristics of a transistor well.

Miller's Theorem states that in a linear circuit, an impedance Z connected between two nodes with a voltage gain A = V₂/V₁ can be replaced by two impedances connected from each node to ground. The equivalent impedances are Z₁ = Z / (1 - A) and Z₂ = Z * A / (A - 1).

Miller capacitance refers to the application of this theorem to the collector-to-base capacitance (C_bc or C_μ) of a BJT. Because the gain A is typically large and negative in an inverting amplifier, the input capacitance becomes C_in,Miller = C_bc(1 + |A|). This is highly relevant in BJT amplifier analysis because it significantly increases the effective input capacitance, which dominates the high-frequency response and limits the bandwidth of the amplifier.