| 摘要 |
A digital to analog converter using pulse width modulation is disclosed. The digital to analog converter according to the invention comprises a PWM pulse generator and an integrator. First, the PWM pulse generator includes a first data buffer 100 and a second data buffer 200. First data buffer 100 is provided with an input terminal for receiving digital signals having control value Din produced by the system controller, for example, in response to a key input. Second data buffer 200 is provided for storing the previous control value Din-1. The new input data stored in first data buffer 100 and second data buffer 200 are compared one another in a controller 600. The controller 600 is provided for receiving the output signal of comparator 500 and for supplying control signals with a pulse generator 300 and a time constant selector 400 based on the comparator output signal. The time constant selector 400 may include a number of resistors which can be selected through an electronic switch in response to the control signal fed from the controller 600. The pulse generator produces a pulse signal in which duty ratio of the pulse signal can be varied by the control signal; also the time constant selector selects a resistance value of the time constant of the integrator which converges the input pulse signal from the pulse generator on a DC voltage value proportional to the duty ratio of the pulse signal. According to this invention, the speeding up of the response time of the analog output signal can be possible by reducing the transient period and also the magnitude of ripple can be reduced which result in enhancing the quality of the output signal.
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