13.68 It is required to derive the expressions in Eqs. (13.87) and (13.88). Toward that end, first find vB7 in terms of vBEN and hence iN. Then find vB6 in terms of iP. For the latter purpose note that Q4 measures vEBP and develops a current i4 = (vEBP − vEB4)/R4). This current is supplied to the series connection of Q5 and R5 where R5 = R4. In the expression you obtain for vB6, use the relationship
to express vB6 in terms of iP and ISN. Now with vB6 and vB7 determined, find iC6 and iC7.