Abrupt junction varactor diode television tuner
AssigneeZenith Radio Corporation
InventorJohn Y. Ma
Life of this patent
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Abstract
A VHF television tuner has four tunable circuits each including an abrupt junction varacto diode having a predictable capacitance tuning voltage characteristic. The VHF frequency spectrum is divided into Lo and Hi bands encompassing television channels 2-14 6 and 7-14 13, respectively. A pair of voltage divider networks comprising precisely trimmed resistive material on a ceramic substrate provide tuning voltage terminals corresponding to the VHF television channels. The end terminals of each divider network are coupled to adjustable potentiometers for setting the tuning voltage at each extreme of the voltage divider. A substrate mounted switch accesses the tuning voltage poins, supplies bandswitching voltages and provides AFC defeat between channels.
Claims21
A tuner for tuning television signals in a predetermined frequency range having a maximum and minimum frequency comprising:
- translation and conversion means for receiving television signals and heterodyning the received signals with locally produced oscillatory signals to produce substantially fixed frequency intermediate frequency signals, said translation and conversion means having an input capacitance which limits high frequency signal gain and including a plurality of stages having tunable circuits each with an abrupt junction type variable capacitance diode for tuning thereof;
- means for imposing tuning voltages on said variable capacitance diodes for simultaneously varying their capacitances to change the tuning of said tunable circuits, said variable capacitance diodes having a capacitance-to-voltage characteristic which is predictable from diode-to-diode and which precludes the need for matching diodes to assure frequency tracking of said tunable circuits with tuning voltage changes on said diodes and being selected to have a capacitance at said maximum frequency that is greater than said input capacitance and a capacitance at said minimum frequency which satisfies the criterion that the gain-bandwidth product of said tuner is substantially constant over said predeterminned frequency band.
A tuner for tuning to transmitted television signals in a frequency range having a given maximum to minimum frequency ratio (F) comprising:
- signal translation means, including an oscillator and mixer for generating a fixed IF signal, having an input capacitance which limits high frequency signal gain;
- a plurality of tunable circuits in said signal translation means each including a variable capacitance diode, said variable capacitance diodes having a capacitance-to-voltage characteristic which is predictable from diode-to-diode and which precludes the need for matching diodes to assure frequency tracking of said tunable circuits with tuning voltage changes on said diodes;
- means for supplying tuning voltages to said variable capacitance diodes for simultaneously adjusting the capacitance thereof, the capacitance voltage characteristic of said variable capacitance diodes determined by ##EQU17## and providing a range of capacitance change Cmax/Cmin determined by ##EQU18## where C.sub.1 and C.sub.2 are the capacitances of the varactor diode at any tuning voltages V.sub.1 and V.sub.2, .phi. is a constant related to the contact potential of the diode, .gamma. is a constant having a maximum value of 0.5, Cmax and Cmin are the maximum and minimum values of tuning capacitance, respectively, and Cs is the stray capacitance of the signal translation means and includes said input capacitance.
An electronic television tuner without a fine tuning control for receiving and translating television signals in a fixed frequency range comprising:
- a plurality of varactor tuned stages, including abrupt junction varactor diodes having capacitance-to-tuning voltage characteristics which are predictable from diode-to-diode and which precludes the need for matching diodes to assure frequency tracking of said tunable circuits with tuning voltage changes on said diodes;
- means supplying tuning voltages to said varactor tuned stages for tuning said tuner to individual television signals in said frequency range;
- a stable voltage divider network comprising a plurality of resistors and voltage terminals at which said tuning voltages are developed;
- and setting means coupled to said voltage divider network for setting the tuning voltage of at least one of said voltage terminals to enable reception and translation of a corresponding one of said television signals.
Dependencies are inferred from the claim text.