How to increase transconductor output swing?

[ray.deng]

I'm on a project to design a bandpass Gm-C filter and one of the requirement spec is Total Harmonic Distortion less than 50dB with two tone input signals at 1v peak-to-peak. As far as I know, transconductor usually has large input and output impedance. Small voltage change at the input will generate a small current change and this current at the ouput node will result in large voltage change. At my case, the output transistor can have only 0.1v change and any further variance will pull it out of saturation. I was just stuck at this issue. Can anyone give me some advice? Thanks.

 

[leo_o2]

Pls add a full-swing buffer stage to extend output voltage range.