Correction: Resistor values used are probably: 100 = 10 ohms 560 = 56 ohms or is it 680 = 68 ohms? 101 = 100 ohms 121 = 120 ohms 181 = 180 ohms 221 = 220 ohms 271 = 270 ohms
Thus the total resistance from the 5V supply to the output terminal of the input device is actually = 220 + 10 + 10 = 240 ohms. Equivalent resistance from input device "source" terminals to ground = 90 ohms. Voltage divider for Vcc of MMIC is 56 ohms from 5V is series with 270 ohms to ground nominal current ~ 15mA + 6mA? for MMIC, total ~ 21mA. Input device if shorted would have a current drain of 5V/(90+220 + 10 + 10) ~ 15mA. Thus measuring the dc output of the input device and/or measuring its power supply current is required to assist diagnosis. Some pHEMT devices have an absolute drain source voltage limit as low as 3V so the operating drain source voltage of the input device may only be 1/2 that. Typical MMICs have a somewhat larger dc voltage on the output. Bruce _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
