• The op amp is configured as an ac amplifier to ease biasing problems
• The diode rectifies the output voltage and applies it to the voltage divider formed by R1, R2
• The Bubba oscillator is another phase shift oscillator
• Four RC sections require –45° phase shift per section
• Very low distortion sine waves can be obtained
• If the Freq. is larger than 4 MHz, the additional Phase-Shift is done by the delay of the Gate.
• The value of CL is approx. 1/ωC where ω=2pf, but not less than about 20 pF.
CIRCUIT 2-3 : Gate oscillator with improved stability
• A small C in series with the xtal acts as the xtal load and isolates the xtal from the rest.
• Ca and Cb are made large to swamp out the effects of Temp. / Supply Voltage change.
• This circuit operates in the parallel mode just as the Pierce oscillator above.
• The resonant circuit LA-CB is an effective short at the fundamental frequency
• It is tuned somewhat below the deferred crystal overtone frequency.
• CL is chosen to suppress operation in the fundamental mode.
• LA may be tuned to produce maximum output.