The Designer's Guide Community Forum

The Designer's Guide Community Forum
https://designers-guide.org/forum/YaBB.pl
Design >> Analog Design >> passive switched capacitor adder
https://designers-guide.org/forum/YaBB.pl?num=1392533658

Message started by jovial on Feb 15^th, 2014, 10:54pm

Title: passive switched capacitor adder
Post by jovial on Feb 15^th, 2014, 10:54pm

I am following your paper "Porrazzo, S.; Morgado, A.; San Segundo Bello, D.; Cannillo, F.; Van Hoof, C.; Yazicioglu, R.F.; van Roermund, A.H.M.; Cantatore, E., "A 155 /spl mu/W 88-dB DR Discrete-Time /spl Delta/ /spl Sigma/ Modulator for Digital Hearing Aids Exploiting a Summing SAR ADC Quantizer," Biomedical Circuits and Systems, IEEE Transactions on , vol.7, no.5, pp.573,582, Oct. 2013".

Can you suggest me the suitable reference to understand the working of the passive SC adder (Fig.4)? A reference providing the full derivation would be very helpful.

Title: Re: passive switched capacitor adder
Post by danmiso on Feb 16^th, 2014, 3:59pm

I don't know any particular reference you are looking for, but the idea is very simple to analyze using charge conservation.

In φ2, Cf0, Cf1, ..., CfL are all fully discharged therefore, the total charge is 0. In φ1, the total charge is expressed as (Xout - X0)Cf0 + (Xout - X1)Cf1 + ... + (Xout-XL)CfL = 0 as the total charge remains 0 (basic physics). Solving the above for Xout, Xout = (Cf1 x X1 + Cf2 x X2 + ... + CfL x XL) / (Cf1 + Cf2 + ... + CfL), a weighted sum of the input voltages.