balanced and fully-diffrential are they the same?

[zoulzubazz]

hey guys,

the aim is to IQ demodulate the signals from a balanced coil. The AD8333 seems suitable for the intended purpose but the datasheet (page 25) suggests that the RF inputs of the chip be driven by fully differential outputs from a Low noise amplifier. Now I am a bit confused about terminology here, attached figure will help the question.



VG1 and VG2 replace the balanced coil illustrated in the left in red, U1, U2, U3 and U4 form the pre-amp stage. does RFN and RFP shown in red and black in the figure represent fully differential signal lines which can drive the RF inputs of the 8333? Thanks very much.

 

[FvM]

Apart from the problem what's a suitable input source for AD8333, the shown amplifier topology looks erroneous in any case. The feedback loop through cascaded amplifiers must be considered unstable.

"Fully differential" is usually designating differential in/out amplifiers, alternatively a transformer could be used.

 

[zoulzubazz]

thanks FvM, the circuit was adopted from a research paper, attached is the picture of the circuit from the article. is there any particular reason the circuit is unstable? the general idea is an instrumentation amplifier with active compensation. thanks.

 

[FvM]

The cascade of G=21 amplifier, voltage divider and amplifier in open loop configuration will give you negative phase margin without additional frequency compensation.