Broadband variable gain amplifier with low group delay variation

In this work a baseband variable gain amplifier (VGA) with a maximum differential gain of 18.2 dB and a 3 dB frequency of 45.9 GHz is presented. The proposed design uses inductive shunt peaking to individually tune the frequency responses of the two gain stages, thus enhancing the overall bandwidth with minimal deterioration of gain and group delay flatness. The phase response in different gain states is analyzed, proving that the cascode stage with parallel transistor is well suited to achieve low group delay variation over a wide gain control range. The circuit fabricated in a 130 nm SiGe BiCMOS technology achieves a group delay variation of only ± 2.8 ps over the gain control range of 18 dB and shows a flat gain response. The VGA consumes a DC power of 205 mW and occupies an area of 0.48 mm ² .