| 摘要 |
PCT No. PCT/GB96/01188 Sec. 371 Date May 4, 1998 Sec. 102(e) Date May 4, 1998 PCT Filed May 17, 1996 PCT Pub. No. WO96/37041 PCT Pub. Date Nov. 21, 1996A local oscillator noise rejection circuit is described which has a resistance between the output of an MES FET/HEMT and ground. This resistance has the effect of introducing a self-biasing arrangement to the oscillator circuit which means that when there is any increase in current through the MES PET/HEMT device, the voltage drop across the resistance also increases. Since the gate is tied to ground via a low resistance (51 OMEGA ) this leads to an increased negative gate to source voltage which causes the device to "pinch-off" slightly which, in turn, gives a reduction in the current level through the device. This arrangement therefore has the effect of reducing any current surges within the device and produces an improvement in phase noise. In a preferred arrangement a 30 Ohm resistor is located between the source of the FET/HEMT and ground, the resistor being located in series within the printed circuit inductor and the output line. With the aforementioned modified circuit, an improvement in the phase noise performance has been measured from the standard circuit which gave a figure of -64 dBc. At 10 KHz. After modification using the above mentioned circuit a figure of -76 dBc. At 10 KHz. was obtained which is approximately a 16 times improvement. |
