| 摘要 |
The frequency range of voltage-controlled oscillator (VCO) of a frequency synthesizer can be expanded so that with a controllable switch (S) either a negative direct voltage -Vb is arranged to the anode of the capacitance diode (D) included in the resonance circuit (L1, D) of the VCO or it is connected, regarding the direct current, to the ground of the circuit, whereby the anode is provided with direct voltage 0 V. On the other hand, when on the cathode of said capacitance diode (D) the control direct voltage Vcntrl, derived from a loop filter (23), is effective, having a given range of variation 0 to Vcntrl,MAX, the voltage range across the capacitance diode is either 0 to Vcntrl,MAX, if 0 V direct voltage is effective on the anode, or it is Vb to (Vcntrl,MAX+Vb), if a negative voltage is effective on the anode. This means that, depending on the anode voltage of the diode, two voltage control ranges can be produced for the VCO, and thus, two frequency ranges, although the external voltage changes only in one range. <IMAGE> |
