A novel general-purpose low-voltage rail-to-rail CMOS(complementary metal-oxide-semiconductor transistor)operational amplifier(op-amp)is introduced, which obtainsconstant transconductance, slew rate and constant high gain overthe entire input common mode voltage range. The proposedscheme has the potential for applications in deep submicrometertechnology, as the operation of the circuit does not exclusivelyrely on the square-law or the linear-law of transistors. The schemeis compact and suitable for applications as VLSI cell. The rail-to-rail op-amp has been implemented in DPDM 0.6 um mixed-signal process. The simulations show that in the entire range ofinput common mode voltage, the variations in transconductance,SR and gain are 1% ,2.3%, 1.36 dB, respectively. Based on this,the layout and tape-out are carried out. The area of layout is0.072 mm2. The test results are basically consistent with thecircuit simulation.