JFET can be used for this purpose...... JFET is operated in the linear region and its GATE voltage is varied suitably to vary its resistance because the curve depends on the Vgs and so the resistance depends on the Vg.........
to get the idea clearly check out..... **broken link removed**
MOSFET can be used as a voltage--controlled,when it operate in linear area,you can get detail information from the Design of Analog CMOS Integrated Circuits by Behzad Razavi\][/i][/quote]