The first circuit is a dual ramp generator where the positive
and negative ramps are generated separately. This circuit
was used as a ramp generator for a transistor curve tracer:
the positive going ramp was used for testing NPN transistors
and the negative ramp for testing PNP transistors.
Generating Triangle Waves
In the circuit to the right, we use a separate integrator to
generate a ramp voltage from the generated square wave.
As a result, we can get both waveforms from a single circuit.
The phase relationship shown between the two output
waveforms is correct
555 ramp generator
Again, we are using a 555 timer IC as an astable multivibrator,
or oscillator. This time, however, we will compare its operation
in two different capacitor-charging modes: traditional RC and
constant-current.
Ramp Generator by Schmitt trigger
The ramp is generated by a constant charging current into
capacitor CRAMP, which is connected between ground and
the noninverting input of op amp IC1, configured as a
voltage follower. The current through RRAMP is the charging
current, kept constant by forcing the voltage across RRAMP
to equal the reference voltage from IC1. One side of RRAMP
is connected to CRAMP, and the other side to the reference
output. In turn, the ground terminal of the reference IC connects
to the op-amp output, which provides a low-impedance replica
of the voltage across CRAMP
capacitor must be charged from a constant current. R1 is
replaced with another PNP Q3, which implements a constant
current source. Q3's base voltage is fed from a diode drop,
leaving just a single resistor R1 to vary the charging current,
and hence frequency of oscillation.
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