Apparatus and methods disclosed herein operate to receive a differential input signal at a first-stage pair of transconductance devices. The differential signal is amplified by a second-order factor at a positive-side or a negative-side first-stage transconductance device, depending upon the polarity of the differential input signal, to create a second-order signal at the output of the appropriate first-stage device. The second-order output signal is then amplified by another second-order factor at a corresponding second-stage transconductance device. A resulting fourth-order signal is made available at an output node as a quartic-response current source. The quartic-response current source may be utilized as a dynamic bias source in conjunction with a linear amplifier to provide a high slew rate amplifier.