?
?ine Canby
hi all,
I need to add two signals, a DC and an AC. The AC signal comes from a
DAC, and I wish to supply the DC signal using a varible resistor pot
on the circuit board. The thing is, I'd like the DC output to be
linear with respect to the pot position. In other words, if I turn the
pot 1 turn and get an output increase of 0.1 Volts, then I'd like to
get a further increase of 0.1Volts when I again turn the pot by one
rev.
I need to attenuate the DAC output by a factor of 2 to obtain the
correct scaled AC value, and I was thinking of using the -15 (to gain
a positive output) rail to obtain an output offset voltage of between
0 Volts and 1.6 Volts. In otherwords, I need to add a DC Voltage of
between 0 Volts and 1.6Volts to my scaled AC value when producing my
output voltage.
If we ignore the AC section of the summing amp for a second and
concentrate on the DC section, we basically hav an inverting amp. The
problem is, how would I introduce a variable resistor into an
inverting amplifier circuit to obtain the linear output I desire?
Obviously the resitor beween the differential input and the output
must remain at a fixed value as it would be shared by the AC section
of the summing circuit. I've tried voltage dividing the -15Volt rail
with two resitors in series(between 0 and -15), and connecting their
intersection to the input resistor of the a typical inverting amp
circuit. Making any of these resistor varing, will not result in a
linear output.
Any suggestions?
Thanks.
I need to add two signals, a DC and an AC. The AC signal comes from a
DAC, and I wish to supply the DC signal using a varible resistor pot
on the circuit board. The thing is, I'd like the DC output to be
linear with respect to the pot position. In other words, if I turn the
pot 1 turn and get an output increase of 0.1 Volts, then I'd like to
get a further increase of 0.1Volts when I again turn the pot by one
rev.
I need to attenuate the DAC output by a factor of 2 to obtain the
correct scaled AC value, and I was thinking of using the -15 (to gain
a positive output) rail to obtain an output offset voltage of between
0 Volts and 1.6 Volts. In otherwords, I need to add a DC Voltage of
between 0 Volts and 1.6Volts to my scaled AC value when producing my
output voltage.
If we ignore the AC section of the summing amp for a second and
concentrate on the DC section, we basically hav an inverting amp. The
problem is, how would I introduce a variable resistor into an
inverting amplifier circuit to obtain the linear output I desire?
Obviously the resitor beween the differential input and the output
must remain at a fixed value as it would be shared by the AC section
of the summing circuit. I've tried voltage dividing the -15Volt rail
with two resitors in series(between 0 and -15), and connecting their
intersection to the input resistor of the a typical inverting amp
circuit. Making any of these resistor varing, will not result in a
linear output.
Any suggestions?
Thanks.