An amplifier includes an amplifying stage, a cascoded circuit, an input feed-forward circuit and an output stage. The amplifying stage is arranged receiving a differential input pair to generate an amplified differential input pair. The input feed-forward circuit is coupled to the cascoded circuit, and is arranged for feeding the differential input pair forward to the cascoded circuit. The output stage is coupled to the amplifying stage and the cascoded circuit, and is arranged for generating a differential output pair according to the amplified differential input pair and an output of the cascoded circuit.

An active current source load of a fully differential amplifier which is converted into a transconductance (g.sub.m) component also at higher frequency by feed-forwarding input signals to their gates. With signal coupling to gate, unity gain bandwidth (UGB) of the amplifier increases by a factor of two. In addition to this, the signal is coupled to source as well to achieve three-fold UGB enhancement. Thus, the effective trans-conductance is g.sub.mp at dc and becomes g.sub.mp+(g.sub.mn.sub.gate+g.sub.mn.sub.src) at high frequency which triples the UGB when g.sub.mp=g.sub.mn.sub.gate/src.

An active current source load of a fully differential amplifier which is converted into a transconductance (g.sub.m) component also at higher frequency by feed-forwarding input signals to their gates. With signal coupling to gate, unity gain bandwidth (UGB) of the amplifier increases by a factor of two. In addition to this, the signal is coupled to source as well to achieve three-fold UGB enhancement. Thus, the effective trans-conductance is g.sub.mp at dc and becomes g.sub.mp+(g.sub.mn.sub.gate+g.sub.mn.sub.src) at high frequency which triples the UGB when g.sub.mp=g.sub.mn.sub.gate/src.

An amplifier includes an amplifying stage, a cascoded circuit, an input feed-forward circuit and an output stage. The amplifying stage is arranged receiving a differential input pair to generate an amplified differential input pair. The input feed-forward circuit is coupled to the cascoded circuit, and is arranged for feeding the differential input pair forward to the cascoded circuit. The output stage is coupled to the amplifying stage and the cascoded circuit, and is arranged for generating a differential output pair according to the amplified differential input pair and an output of the cascoded circuit.

An interface circuit configured in accordance with certain aspects of this disclosure has a high-pass filter and a low-pass filter. The high-pass filter may include a capacitor coupled between an input of the interface circuit and an output of the interface circuit and a resistor coupled between the output of the interface circuit and a voltage reference source. The capacitor and resistor may be configured to provide a low-pass filter that couples the reference voltage source to the output of the interface circuit. The interface circuit provides a feedforward loop that includes the reference voltage source and an amplifier. The amplifier has an input coupled to the input of the interface circuit and an output coupled to the reference voltage source.