US Patent 7847638 Cascoded circuit

A cascoded current-mirror circuit includes a first N channel MOS transistor, a second N channel MOS transistor, a third N channel MOS transistor and a fourth N channel MOS transistor. The first N channel MOS transistor and the second N channel MOS transistor are cascode-connected between a higher voltage source and a lower voltage source. The third N channel MOS transistor and the fourth N channel MOS transistor are cascode-connected between the higher voltage source and the lower voltage source. A drain of the first N channel MOS transistor is connected to gates of the first N channel MOS transistor, the second N channel MOS transistor, the third N channel MOS transistor and the fourth N channel MOS transistor. The threshold voltages of the second N channel MOS transistor and the fourth N channel MOS transistor are larger than those of the first N channel MOS transistor and the third N channel MOS transistor.