AN INTEGRATED TRANSMISSION-GATE DAMPING RESISTOR FOR MOS CRYSTAL OSCILLATORS
Original Publication Date: 1990-Oct-01
Included in the Prior Art Database: 2001-Nov-21
MOS IC's frequently contain a crystal oscillator to provide clocking. Typically, a linear amplifier (comprised of a digital inverter biased by the feedback resistance of an "on" transmission-gate connected between the inverter input and output) and clock buffers are integrated on the IC, while the crystal and loading capacitors are implemented discretely external to the IC. In addition, crystal vendors often recommend placing a damping resistor in series with the amplifier output to (1) decrease the current injected into the crystal to prevent crystal damage, (2) stabilize the resonant circuit by reducing coupling from the amplifier and (3) reduce the possibility of spurious oscillations at crystal overtones by decreasing the high frequency loop gain. Despite these advantages, the damping resistor is usually excluded to avoid the added cost and area of a descrete resistor.