A BJT differential amplifier operating with a 0.5-Ma current source uses transistors for which β = 100, fT = 500 MHz, Cμ = 0.5 pF, and rx = 100Ω. Each of the collector resistances is 10 kΩ, and ro is very large. The amplifier is fed in a symmetrical fashion with a source resistance of 10 kΩ in series with each of the two input terminals.
(a) Sketch the differential half-circuit and its high-frequency equivalent circuit.
(b) Determine the low-frequency value of the overall differential gain.
(c) Use the Miller approximation to determine the input capacitance and hence estimate the 3-dB frequency fH and the gain-bandwidth product.