current-to-voltage converter-transistance

Miller capacitance C_M

As most amplifiers are inverting (i.e. A_v < 0), the effective capacitance at their inputs is increased due to the Miller effect. This can lower the bandwidth of the amplifier, reducing its range of operation to lower frequencies.

Mitigation

A current buffer stage may be added at the output to lower the gain A_v between the input and output terminals of the amplifier (though not necessarily the overall gain). For example, a common base may be used as a current buffer at the output of a common emitter stage, forming a cascode. This will typically reduce the Miller effect and increase the bandwidth of the amplifier.
Alternatively, a voltage buffer may be used before the amplifier input, reducing the effective source impedance seen by the input terminals. This lowers the RC time constant of the circuit and typically increases the bandwidth.