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hello mike and aryajur,
I believe that you should ground Rf at both input and output sides when calculating the open-loop gain A. Please refer to Sedra & Smith, 5th edition, example 8-3.
dithering pll
I am designing a fractional-N PLL, with a MASH 1-1-1 sigma-delta modulator. I simulated the SDM with Matlab, and saw that there were spurs (idle tones) at the output. I added a pseudo-random bit generated by LFSR to the LSB of the SDM input, but the spurs remain. Seems that the...
hi all,
I am quite confused of the noise spec such as noise figure and root mean square noise voltage. And, how to measure them? Can you provide me some reference?
Thanks.
current mirrors are used to duplicate currents, not to generate them.
You need current sources to generate robust currents, then you can use current mirrors to duplicate them.
The picture you uploaded is indeed a combination of current source and a current mirror. The current source formed by...
You should use resister with smaller temperature coefficient. If you can measure the value of any one of the resistor on chip (of the same type to the one you used in the bias block), you can figure out the problem.
pll loop bandwidth
I think you can refer to :
https://www-mtl.mit.edu/researchgroups/perrottgroup/Publications/Talks/MTT_2004_meninger.pdf
The transfer function of each noise source to the vco output is different. The noise coming from PFD/charge pump is low-pass filtered, and the noise from...
1. I think when the ratio is larger, the difference between vin+ and vin- gets smaller, maybe because of bias condition, and it makes the matching better.
2. Yes, for an opamp with vout connected to vin-, the loop gain is (roughly) the open loop gain of the opamp. I said "roughly" because the...
I meant, if the source follower M3 is included in the opamp, and M1 & M2 are the bias circuit, the output of the opamp is the source of M3, which only drives vin-. (M4 seems can be negligible when analysing stability.)
1. I think you need larger loop bandwidth.
2. 7nA is quite a small amount...
Originally the load is the gate capacitance of M3.
But if you include M3, the source follower, into the OPamp, the output (source of M3) is directly feedback to vin-. The question is to design the unity-gain buffer formed by the OPamp, with no more load to drive.
How do you think?
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