Step attenuator using PIN diodes

A step attenuator using a PIN diode for use with microwave circuits. The step attenuator circuit provides for stepwise controlling the current applied to the microwave monolithic integrated circuit. The step attenuator circuit comprises a driver circuit and a attenuator circuit coupled thereto. The driver circuit that comprises a temperature sensor, a comparator circuit coupled to the temperature sensor for comparing the temperature value sensed by the temperature sensor to predetermined reference voltages and for providing a plurality of output signals that are indicative of a respective plurality of temperature values sensed by the temperature sensor, and a resistor network coupled to the comparator circuit that is adapted to set the respective values or current provided by the driver circuit. The attenuator circuit comprises a PIN diode coupled to the microwave circuit (MIC or MMIC) that has the temperature sensor coupled thereto, a plurality of resistors respectively coupled to receive the plurality of output signals from the comparator circuit, and a resistor coupled between the plurality or resistors and the PIN diode. Alternatively, a lambda /4 microstrip circuit may be used in place of the single resistor. Attenuator bits (4 bits, for example) are controlled by the PIN diode driver that determines the current on each bit. The step attenuator provides temperature compensation for a chain of microwave amplifiers. For example, an amplifier chain containing two MMIC amplifiers may vary 4 dB in overall gain over the range of -55 degrees C. to +71 degrees C. When the gain drops by 1 dB, an attenuator bit turns off, increasing the gain up to a nominal value. When the gain increases by 1 dB (as temperature decreases), an attenuator bit turns on, decreasing the gain down to the nominal value. The present step attenuator may use two PIN diodes in a balanced design.