a programmable gain mos amplifier is disclosed . the programmable gain mos amplifier is capable of increasing its programmable gain linearly in db unit by increasing its gain level data linearly . the programmable gain mos amplifier includes a plurality of gain providers for providing predetermined gains respectively , and a plurality of gain tuners . each of the plurality of the gain tuners is disposed for adjusting the predetermined gain from the corresponding gain provider . each of the gain tuners includes a gain enabling module and a gain decreasing module . the gain enabling module allows the corresponding predetermined gain to add to the programmable gain of the mos amplifier . the gain decreasing module declines the corresponding predetermined gain added to the programmable gain of the mos amplifier .