Ramp generators typically generate sawtooth waveforms and are used in a myriad of applications. For example, sawtooth waves are, among other things, perhaps best known for their use in music waveform generation. Another application of ramp generators is in power conversion systems using pulse width modulation. Power converters may frequently be used to power loads having tight regulation characteristics. To provide voltage conversion and regulations, the power converters may use active switches that are coupled to a voltage source and periodically switch a reactive circuit element (e.g., inductor) to the voltage source at a switching frequency in the order of a few MHz or lower. Accordingly, controllers employing ramp generators may be required to manage the operation of the power convertors by controlling the conduction periods of the switches employed in the power converter.
Ramp generators creating sawtooth waveforms may also be employed to produce vertical and horizontal deflection signals used to generate a raster on CRT-based television or monitor screens. Oscilloscopes also use a sawtooth waveform for their horizontal deflection, though they typically use electrostatic deflection. On the sawtooth waveforms ramp portion, the magnetic field produced by the deflection yoke drags the electron beam across the face of the CRT, creating a scan line. On the sawtooth waveforms cliff, the magnetic field suddenly collapses, causing the electron beam to return to its resting position as quickly as possible. Thus, a linear ramp and sharp cliff may be desired.
FIG. 1 illustrates a conventional ramp generator, as known in the art. As depicted, an operational amplifier based integrator 100 may include an operational amplifier (Op Amp) 102, an input resistor 104, and a capacitor 106 located within the negative feedback path between the output terminal 108 and the negative input terminal 110 of the Op Amp 102. The capacitor 106 and resistor 104 determine the RC time constant of the integrator 100, whereby based on relationship 105 (also recited below), the integrator 100 integrates input square wave 112 in order to generate output ramp signal 114.
      V    out    =            -                        ∫          0          t                ⁢                              (                                          V                in                            /              RC                        )                    ⁢                                          ⁢                      ⅆ            t                                +          V      intial      
For example, the high level of ramp generator 100 may be set to a voltage potential that is higher than ground, while the low level may be set to be below ground (i.e., a negative voltage). As depicted, the ON_Period of the input square wave 112 may result in a downward slope ramp portion 118a of output signal 114, which may be generated based on the plate of the capacitor 106 at the negative terminal building positive charge and the other terminal of the capacitor 106 at Vout building negative charge. Conversely, during the OFF_Period of the input square wave 112, the capacitor 106 charges up to produce upward slope ramp portion 118b of output ramp signal 114. Thus, a triangular type waveform may be generated. In contrast with a desired sawtooth waveform profile, based on the finite discharge time requirement for capacitor 106, the output ramp signal 114 may fail to exhibit a sharp or steep drop to ground or another designated reference voltage.
It may, therefore, be advantageous, among other things, to provide an enhanced ramp generator for optimizing the generation of saw tooth waveforms over various clock frequencies.