Datasheet LT1671 (Analog Devices) - 10

LT1671
U U W U APPLICATIONS INFORMATION Crystal Oscillators Switchable Output Crystal Oscillator
Figure 7 shows a crystal oscillator circuit. In the circuit, the Figure 8 permits crystals to be electronically switched by resistors at the LT1671’s positive input set a DC bias point. logic commands. This circuit is similar to the previous The 2k-0.068µF path sets up phase shifted feedback and examples, except that oscillation is only possible when the circuit looks like a wideband unity-gain follower at DC. one of the logic inputs is biased high. The crystal’s path provides resonant positive feedback and stable oscillation occurs. XTAL X RX LOGIC INPUTS AS MANY STAGES AS DESIRED XTAL B D 5V X 1k B 1MHz TO 10MHz 2k 5V CRYSTAL (AT-CUT) XTAL A 1k A 1k D1 D2 + + LT1671 OUTPUT LT1671 OUTPUT 1k 2k – – 2k 2k 1671 F08 1671 F07 75pF 0.068µF = 1N4148 GROUND XTAL CASES
Figure 7. 1MHz to 10MHz Crystal Oscillator Figure 8. Switchable Output Crystal Oscillator. Biasing A or B High Places Associated Crystal in Feedback Path. Additional Crystal Branches Are Permissible
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