A voltage-controllable linear MOS transconductor using bias offset technique

A linear large-signal MOS transconductor with the gain adjustable linearly by a voltage is described. A perfect linear transfer characteristic is obtained by two cross-coupled differential transistor pairs operating in saturation pairwise at unequal bias, offering offset-free operation, with both differential or single-ended input and differential output. Single-ended output is achievable by use of a current mirror. The nonlinearity caused by mobility reduction, channel-length modulation, mismatch, etc. is discussed. A test circuit with transconductance of 6.25 mu mho has been built with 3- mu m MOS components, and a linearity error of less than +or-1% was measured for an input voltage range from -4 to 4 V.<
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