Digital to analog converter television tuning of varactor tuners

Claim 2

In a television tuning system: a tuner including a varactor diode; a variable resistor, said tuner being tunable by tuning voltages supplied to said varactor diode from said variable resistor; channel selection means for digitally selecting any channel by decade and unit selection; first electronic digital to analog converter means for establishing coarse tuning voltages defining a relatively broad tuning range in response to said decade selections; and fine tuning range means effecting limited and substantially equal fine tuning ranges for all channels comprising; second electronic digital to analog converter means responsive to said unit selection for providing a control effect in accordance with the selected unit; voltage dividing means including said variable resistor coupled to said first electronic means and to said second electronic means to derive from said coarse tuning voltages fine tuning voltages which define limited and substantially equal fine tuning ranges for all unit selections; said voltage dividing means including electronic switching means coupled to said second electronic means and in circuit with said variable resistor; said electronic switching means operable in accordance with said control effect to change the potential supplied across said variable resistor; and means coupling the variable element of said variable resistor to said varactor tuner.

Claim 3

A television tuning system in accordance with claim 1 wherein said electronic switching means comprises a plurality of FET switches, each said FET switch having an impedance element coupled thereacross, said FET switches selectively bridging certain ones of said impedance elements in respOnse to said control effect to derive said fine tuning voltages from said coarse tuning voltages.

Claim 4

In a television tuning system comprising a tuner including a varactor diode; a variable resistor, said tuner being tunable by tuning voltages supplied to said varactor diode from said variable resistor, channel selection means for digitally selecting channels by decade and unit selection, first electronic digital to analog converter means for establishing coarse tuning voltages defining a relatively broad tuning range in response to said decade selections, and second electronic digital to analog converter means for effecting limited and substantially equal fine tuning ranges for all channels in response to said unit selections comprising: a plurality of FET switches, each having a gate input and a pair of main terminals, with the main terminals of said switches coupled together to form two sets of serially connected switches, one end of each said set of serially connected switches coupled to said first electronic means; means coupling said variable resistor between said two sets of serially connected switches; a resistance coupled across the main terminals of each said FET switch; and means coupling said gate inputs to said second electronic converter means for activating certain ones of said resistances in response to said unit selections and thereby derive from said coarse tuning voltages fine tuning voltages defining limited and substantially equal fine tuning ranges across said variable resistor for all said unit selections.

Claim 5

In a television tuning system comprising a tuner including a varactor diode; a variable resistor, said tuner being tunable by tuning voltages supplied to said varactor diode from said variable resistor, channel selection means for digitally selecting channels by decade and unit selection, first electronic digital to analog converter means for establishing coarse tuning voltages defining a relatively broad tuning range in response to said decade selections, and second electronic digital to analog converter means for effecting limited and substantially equal fine tuning ranges for all channels in response to said unit selections comprising: a plurality of FET switches, each having a gate input and a pair of main terminals, with the main terminals of said switches coupled together to form two sets of serially connected switches, one end of each said set of serially connected switches coupled to said first electronic means; means coupling said variable resistor between said two sets of serially connected switches; a resistance coupled across the main terminals of each said FET switch; and means coupling said gate inputs to said second electronic converter means for activating certain ones of said resistances in response to said unit selections and thereby derive from said coarse tuning voltages fine tuning voltages defining limited and substantially equal fine tuning ranges across said variable resistor for all said unit selections.