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This Design Idea demonstrates a simple way to turn a step input into a ramp of nearly constant slew rate. The basic circuit uses a single op-amp; a circuit built on an integrator will typically require three.
Figure 1 shows the basic circuit.
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Figure 1 Ramp generator
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The op-amp is wired as a voltage follower, with D1 & D2 clamping the input to one diode drop above or below the output. 
When the input step-changes by a volt or more, the diodes will keep the voltage across R2 at a nearly constant 0.3V (because the output will follow any change on C), creating a constant slew rate at the output of 0.3V/R2C1 V/s. The output will slew to within 0.3V of the input and then follow an RC ((R1+R2)C1) curve until reaching a final value equal to Vin. For best results, R2 should be larger than R1, preferably by factor of ten or more. This simple circuit gives best results with fairly large steps, where the slow settling time won't be objectionable.
Figure 2 adds an extra amplifier to make the output slew to within a few millivolts of the input.
Figure 2 Improved ramp generator
Amplifier U2 amplifies the difference between the input and the output so as to keep the diode clamp operating until the output voltage 
nearly reaches the input. The output will slew to within the diode forward voltage divided by the gain of U2 (that is, 1+(R3/R4)). If the gain is made too large, the circuit will become unstable. The slew rate of U2 should be at least ten times (the higher the better) the output slew rate times the gain of U2. U2 needs extra headroom to keep D1 & D2 conducting, which usually means restricting the input so that it is more than one volt away from the max/min output swing of U2.
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“Neat idea. A1 is actually U2?”
“Pretty handy. good tutorial. “
“Great Information!”
“I used this idea already in 2002 in a motor speed controller. Make R2 adjustable (ideally a log potentiometer) and you can adjust the ramping speed of the motor or whatever you control. If the integration time constant is fairly slow (1/f about 100Hz or
“OOps.. I ment U2 could oscillate…nnChristian”
“This circuit is actually known a “bootstrap” ramp (or sweep) generator. It has been used since vacuum tube days, but has evolved through slightly different configurations depending on the active device. But they all operate using similar principles.
“Linear ramp generator uses one op-amp is a very interesting method to test power supply performances is to measure the open-loop gain and phase to find the gain and phase margin. This measurement will tell you how far from instability you are.nnAndynh
“Ooops…fixing…”