| 摘要 |
PURPOSE: A controller for voltage controlled oscillator and method thereof is provided to enable users to vary free running frequency of the voltage controlled oscillator only when small input terminal is required without using a Zener diode. CONSTITUTION: A controller for voltage controlled oscillator includes the following components. An input buffer(20) buffers a primary digital signal(Z1) and outputs the buffering results as a primary variable signal(B1) in response of a control signal(ZC). A series of primary to N-1 inverters(22, 24, 26,..., 28) inputs each series of secondary to N digital signal(Z2,...,ZN) and reverses them. A series of primary to N-1 inverters (22, 24, 26,...28) outputs each result of reverse process as secondary to N variable signals(B2,...BN). A variable resistance varies resistance values in response to the series of primary to N variable signals(B2,...BN). A method for controlling voltage controlled oscillator includes the following steps. Determining continuously whether the logical level of the control signal is appropriate. Buffering the primary digital signal and determining the logical level of the primary variable signal if the logical level is appropriate. Determining the logical levels of the secondary to N variable signals after reversing the secondary to N digital signals. Holding the determined levels which were previously selected for primary to N variable signals if the control signal is not in the appropriate logical level. Determining the resistance value according to the logical levels of the primary to N variable signals.
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