| 摘要 |
PURPOSE:To make the constitution simple and to enhance the demodulation sensitivity, by detecting the phase by utilizing the fact that the impedance between the drain and the source of an FET is much changed when the DC bias voltage of the gate of the FET is changed. CONSTITUTION:A gate bias voltage is so adjusted that the impedance between the drain and the source of an FET2 is conformed with the characteristic impedance of a band-pass filter 4. The length of a transmission line 5 is set to such value that the phase is shifted by pi/4 in a local signal frequency. The length of a transmission line 6 is set to such value that the phase of the signal passing through this line 6 is shifted from the signal, which is applied to a drain D of the FET2 through the band-pass filter 4 and the transmission line 5 in the local signal frequency by pi/2. The center frequency of the band-pass filter 4 is the frequency of the local signal. Therefore, since local frequency signals applied to the drain D and a gate G of the FET have pi/2 phase difference, the DC output is zero at this point. When the frequency is changed to deviate the phase difference between signals applied to the drain D and the gate G from pi/2, the DC voltage is changed, and the DC voltage is maximum when they are in the same phase. |
