spcecdt@deeptht.UUCP (John DuBois) (12/23/90)
I'm looking at the sheet for the MC1437 dual op-amp. Each op-amp has two connections for "input lag". Unfortunately this Motorola databook gives no indication of their purpose. Does anyone know what they are for? Thanks... John DuBois spcecdt@deeptht.santa-cruz.ca.us
whit@milton.u.washington.edu (John Whitmore) (12/25/90)
In article <116@deeptht.UUCP> spcecdt@deeptht.santa-cruz.ca.us (John DuBois) writes: > > I'm looking at the sheet for the MC1437 dual op-amp. >Each op-amp has two connections for "input lag". >Does anyone know what they are for? Thanks... The MC1437 is not an internally compensated op amp, so... a cookbook amplifier made with the MC1437 will oscillate at some high frequency (instead of amplifying). One can obviously add a filter to the feedback network, but it is simple to tap off a few places inside the amplifier where the impedance is relatively high. The 'input lag' connects to a 25k ohm impedance point in the amplifier, so a relatively small capacitor (to the 'output lag') will suffice to stop oscillation if placed there, and the feedback components can be changed WITHOUT changing the compensation capacitor. The word "lag" refers to the phase-lag of the compensation scheme; some compensations are possible with 'lead-lag' networks for special purposes. Externally compensated op amps are very useful for making low-noise preamplifiers (one can add an input stage and correct the compensation for the extra gain), for high-frequency amps (where one can make an exact choice of compensation for the particular gain), BUT no one would want to use the MC1437; it's not a very good design, compared to even the old-fashioned uA748 (aka "MC1748"). John Whitmore