Precision Crystal Oscillator

48 from an idea by R Shankar When designing oscillators, it is good practice to ensure minimum capacitance of the active element(s), since any parasitic loading of the crystal is bound to derate the overall stability to some extent. This forms the underlying prin- ciple of the design described here, albeit that good results are also obtainable when an additional load capacitance is connected in parallel with the existing parasitic capacitance, N1 ... N3 = 1/2 IC 1 = 74 LS 04, 74 HC(U) 04 OSCILLATOR C2 40p •• R11 R12 crystal but only if the former is known to possess a low loss factor and a low temperature coefficient, i.e., if it is a very high quality capacitor (and possibly difficult to obtain). The oscillator proposed here is a Pierce type, in which the crystal operates in parallel mode. The input is formed by a bootstrapped source follower, DG MOSFET Tl, which has a parasitic capacitance of only 1 pF. RF transistors T2-T3 are set up as a cascode amplifier. A type BF494 tra...