Hey,
Working on a little project measuring inductors I've pretty much got the design down, but there is one part which is bugging me, and would make the rest a lot easier.
Its a standard window comparator (albeit two independent high speed comparators) with a fixed window width, and variable window centre.
When I say fixed, I mean, say centred at 2v, with a window of 1v (1.5v to 2.5v). Or a window of 2-3V, centred at 2.5.... but with the centre voltage variable to say 4v (3.5V to 4.5V same 1v window width). The standard 3-resistor ladder found in many circuits (including the 555 timer) is out of course, because this produces thresholds as a fraction of the input/reference voltage.
I could use two DAC's to set the thresholds, but this takes time (>20us) as they will be controlled by a micro-controller) although I'll probably end up using a DAC to set the centre anyway.
I cannot think of a way to do with in analogue, but I'm sure it can be done! So far the only workable thing I have is using analogue multiplexers, such as the 74HC4052, to switch between precision resistors which form a divider, with a precision reference. This means, two of these can produce discrete voltage levels, but is quite limited. Which are based off the input reference... again a fraction of this, but clever use of resistor values means I have two sets of voltage levels, with 1V between them.
Ideally it would have a voltage in to set the 'centre' of the window, and resistors (or a pot) to set the width - precision of the width is more important. I know its a tall order, but just wondering if anyone has any design idea's or applications similar? Because the comparator will be working with an input ram signal of >100kHz and will vary this centre voltage on the fly, manually doing it is far too slow
Cheers!
Blueteeth
Working on a little project measuring inductors I've pretty much got the design down, but there is one part which is bugging me, and would make the rest a lot easier.
Its a standard window comparator (albeit two independent high speed comparators) with a fixed window width, and variable window centre.
When I say fixed, I mean, say centred at 2v, with a window of 1v (1.5v to 2.5v). Or a window of 2-3V, centred at 2.5.... but with the centre voltage variable to say 4v (3.5V to 4.5V same 1v window width). The standard 3-resistor ladder found in many circuits (including the 555 timer) is out of course, because this produces thresholds as a fraction of the input/reference voltage.
I could use two DAC's to set the thresholds, but this takes time (>20us) as they will be controlled by a micro-controller) although I'll probably end up using a DAC to set the centre anyway.
I cannot think of a way to do with in analogue, but I'm sure it can be done! So far the only workable thing I have is using analogue multiplexers, such as the 74HC4052, to switch between precision resistors which form a divider, with a precision reference. This means, two of these can produce discrete voltage levels, but is quite limited. Which are based off the input reference... again a fraction of this, but clever use of resistor values means I have two sets of voltage levels, with 1V between them.
Ideally it would have a voltage in to set the 'centre' of the window, and resistors (or a pot) to set the width - precision of the width is more important. I know its a tall order, but just wondering if anyone has any design idea's or applications similar? Because the comparator will be working with an input ram signal of >100kHz and will vary this centre voltage on the fly, manually doing it is far too slow
Cheers!
Blueteeth