Patent ID: 7602327

Claim:
A digitally controllable resistor comprising: a substrate; at least one digitally controllable resistance stage formed on said substrate, each of said at least one stages including: a first resistor connected in series with a switch; a second resistor connected in parallel with said first resistor and said switch; and a control line connected to said switch for opening and closing said switch in response to a control bit associated therewith; wherein said at least one digitally controllable resistance stage includes a plurality of digitally controllable resistance stages connected to one another in series and further wherein said control line provides a control word having a bit associated with each of said plurality of digitally controllable resistance stages; wherein a total resistance of the digitally controllable resistor changes substantially linearly with a value of the control word; wherein for each of said plurality of digitally controllable resistance stages n, a resistance value of said first resistor (R n,down ) is calculated as: R n , down = R min N ⁢ ( R min N · 2 n · Δ ⁢ ⁢ R + 1 ) - R switch and a resistance value of said second resistor (R n,up ) is calculated as R n , up = R min N + 2 n ⁢ Δ ⁢ ⁢ R where R min is a minimum total resistance of said digitally controllable resistor, ΔR is a step resistance of said digitally controllable resistor, N is a number of said plurality of digitally controllable resistance stages and R switch is an on resistance of said switch.