MMIC : Phase shifters and amplifiers

This article describes monolithic microwave integrated circuits that control the phase and amplitude of microwave signals.

Electronically scanned antennas use hundreds of modules, for which the phase and amplitude of the transmitted signal must be controlled for each individual module. For digital transmissions on microwave carriers (from radiotelephones to radio local loops), the modulations used, whether phase shift keying (PSK) or quadrature amplitude modulation (QAM), involve controlling numerous phase shifts as well as the amplitude of the signal in the modulators and demodulators. Finally, replacing filters in transmit and receive heads with local oscillator suppression or image frequency suppression circuits also requires the introduction of phase shifts or phase differences. These considerations show the great interest in studying the different phase-shifting techniques that can be introduced in MMICs (Monolithic Microwave Integrated Circuit). This is the subject of the first paragraph.

Furthermore, the amplitude of the signal, either on reception, transmission or during processing, often needs to be controlled, which requires the use of cells with variable attenuation or gain.

But amplification remains the essential function of all these circuits. This is done in small-signal amplifiers, where the important variables are gain and noise figure (see 2 ). Noise factors close to 1 enable very weak signals to be received, thus increasing link distances or reducing transmission power. Broadband amplifiers can be used for microwave applications such as countermeasures, but these circuits can also amplify digital signals to tens of Gbit/s.

The amplification function is also found in power amplifiers, where the important variables are gain, non-linearities, output power and electrical efficiency (see 3 ). For example, comparative tests on cell phones show that transmit-receive operating times are highly variable. These times are...