I'm in the middle of an extremely complicated (and difficult) project but in this stage I need help with a relatively simple concept. I have designed a sample-and-hold circuit and a comparator circuit but I need a buffer in-between the two to prevent the comparator from drawing too much current from the sample-and-hold.
If you'll look at the attachment you can see I'm using a matched pair of two n-channel JFETs (model to be determined). The top is a source follower and I'm using the bottom as an active load for the follower. I'm trying to get the output voltage to equal the input voltage (or be very close).
If I'm understanding correctly then the current through the bottom JFET must be equal to the current through the top JFET. To that end I'm thinking that the resistance presented to the source of J1 by R12, R4 and R5 and maybe the input resistance of Q6 must be equivalent to the resistance at the source of J2 which is simply R13. However I'm not really sure how to calculate what's the resistance at the source of J1.
Am I using the right approach here? If so how can I calculate the resistance presented to the source of J1?
If you'll look at the attachment you can see I'm using a matched pair of two n-channel JFETs (model to be determined). The top is a source follower and I'm using the bottom as an active load for the follower. I'm trying to get the output voltage to equal the input voltage (or be very close).
If I'm understanding correctly then the current through the bottom JFET must be equal to the current through the top JFET. To that end I'm thinking that the resistance presented to the source of J1 by R12, R4 and R5 and maybe the input resistance of Q6 must be equivalent to the resistance at the source of J2 which is simply R13. However I'm not really sure how to calculate what's the resistance at the source of J1.
Am I using the right approach here? If so how can I calculate the resistance presented to the source of J1?
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