Incrementally adjustable capacitor unit for tuning a crystal-controlled oscillator

Claim 1

In combination with a crystal-controlled oscillator, an incrementally adjustable capacitor unit for tuning the crystal oscillator throughout a relatively broad total range to a desired value, in minute steps each of which produces a like incremental change in the frequency of the oscillator said unit comprising: a. a bank of capacitors having a predetermined number of capacitors whose respective values are in a binary ratio series, the smallest capacitor value in the bank being chosen to satisfy the required frequency adjustment resolution, the sum of all values in the series satisfying the required total range of frequency adjustment, and b. selective switching means for connecting the capacitors in said bank in parallel relation to produce an output capacitance whose lowest value is equal to the value of the smallest capacitor, whose highest value is equal to the sum of the capacitor values and whose intermediate values depend on which switching means are operative, said switching means being constituted by a group of switches equal in number to the number of said capacitors, each switch in the group being connected in series with a corresponding capacitor in the bank to produce a series circuit therewith, the series circuit formed by the bank of capacitors and the group of switches being connected in parallel relation to said crystal oscillator whereby said oscillator is tunable throughout said total range in equi-spaced steps running from the lowest to the highest frequency in the range, the magnitude of each step being equal to the change in frequency produced by the smallest capacitor value in the bank, said capacitors being constituted by a dielectric layer formed on a conductive chip body, the conductive body forming a common rear face electrode, with separated front face electrodes whose dimensions determine the capacitance values in said binary series, said chip being mounted on a Printed circuit board having a conductive base plate, said circuit board having conductive connections leading to said front face electrodes, said group of switches being formed by switching screws extending through the printed board and threadably received in said base plate, said screws, when fully extended, acting to engage said conductive connections to complete a circuit to the base plate.