A method of controlling and maintaining a constant slew rate at an output of a buffer is provided. The method includes the following steps: (a) receiving, (i) a first input signal and (ii) at least one of a control voltage using the buffer; (b) generating a threshold voltage using a first reference voltage generator; (c) comparing (i) the threshold voltage with an output of the buffer using at least one of a comparator; (d) determining a phase difference using a phase detector; (e) producing a DC voltage using a loop filter; (f) generating a reference voltage; (g) receiving the DC voltage and the reference voltage using an amplifier; (h) amplifying the difference between (a) said DC voltage, and (b) the reference voltage to obtain a control voltage using the amplifier; and (i) feeding the control voltage to the buffer.