The following circuit is an inverting comparator with Hysteresis that uses inter

Question

The following circuit is an inverting comparator with Hysteresis that uses internal positive feedback. Assume V_DD=5 V., V_ss = 0 V, (ground). Assume I_BIAS = 20 mu A, (W/L)_L = 10/1, (W/L)_5 = 40/1, (W/L)_3 = 20/1, (W/L)_3 = 20/1, (W/L)_3)=(W/L)_4 = 5/1. (W/L)_7=(W/L)_7 = 45/1, Ignore body effect (y=O) and channel length modulation effect (Lambda = 0) for this problem. Let's set v_i1 = 2 V and vary v_12 from 0 to 5 V. Determine the positive trip voltage V_TRP^- for which the positive feedback start. Now let's vary v, _i2 from 5 V to 0 V. Determine the negative trip voltage V_TRP^- for which the positive feedback starts. You may use the symmetry of the circuit to avoid unnecessary calculations. Plot V_o2 as a function of v_i2 Make sure to compute v_o2 for the following v_i2 = 2 V, v_i2 = 2+V_TRP^+ and v_TRP^-. What is the input common-mode range: +1CMR, -1CMR?

Explanation / Answer

(1) it is given that Vi1 = 2v , Vi2 = 0 to 5 V

VTRP+ = Vi1 / Vi1 + Vi2

= 2 / 2+5 = 2 / 7

(2) given that Vi1 = 2v , Vi2 = 5 to 0 V

VTRP- = -Vi2 / Vi1 + Vi2

= - 5 / 2 + (-5) = -5 / -3

(3) V02 (for Vi2 = 2v) = Vi2 / Vi1 + Vi2

= 2 / Vi1 + 2

V02 (for Vi2 = 2+Vtrp+) = Vi2 / Vi1 + Vi2

= 2+ VTRP+ / Vi1 + 2+ VTRP+

   V02 (for Vi2 = 2+Vtrp-) = Vi2 / Vi1 + Vi2

= 2+ VTRP-/ Vi1 + 2+ VTRP-

(d) ICMR is the range of input DC voltage range for which the circuit is in saturation.

+ICMR = ( Vi1 + Vi2 ) / 2 + ( Vi1 - Vi2 ) / 2

   -ICMR = ( Vi1 + Vi2 ) / 2 + ( -(Vi1 - Vi2) ) / 2

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