as the picture shows, the first reference circuit generates a global 1.5v voltage for the whole chip, then in ir receiver module, there is another reference circuit using 1.5v to generate the voltage of ir module (1.45v, 1.2v, 0.75v, 05v, 0.1v), and at every node, there is a 1pF mos cap. when simulating the first reference with bandgap seperately, it works well; when simulating the ir module with the second reference circuit (with ideal voltage source vdc=1.5v at second reference input), the ir module works well too; but when i simulate the whole circuit as the picture shows (first 1.5v reference + second reference + ir module), the dc operating point is of non-convergence, and the 1.5v voltage becomes to 2.1v (vdd=3v) for 3v/ss/-40deg corner, becomes to 1.04v for 2.7v/ss/-40deg, and other undesired value for other corner. very strange, i wonder why. what is the possible reason? thanks.