Digital-analog driver for brushless D.C. spindle motor

A digital-analog driver circuit for a three-phase wound, brushless D.C. spindle motor for a disk drive including commutation phase generation means for generating digital commutation control signals for the three phases, the driver circuit comprising:

• logic means responsive to the commutation control signals for generating commutation gating signals,
• digital function generation means responsive to a commutation gating signal supplied by the logic means and further responsive to a high frequency clocking signal, for generating a pulse width modulated digital function signal having a base period of the high frequency clocking signal and timed interval synchronized to the commutation gating signal and for supplying the digital function signal to the logic means,
• the logic means including function signal inversion means for generating an inverted digital function signal, and having gating circuit means for selectively putting out the digital function signal and the inverted digital function signal in synchronism with the commutation gating signal,
• speed control signal generation means for generating plural speed control signals corresponding to desired rotational speed of the brushless D.C. motor,
• three digital to analog conversion means each for converting the digital function signal and the inverted digital function signal into an analog phase driving signal,
• pulse height, pulse width modulator means connected between the logic means and the digital to analog conversion means, the modulator means for multiplying each digital function/inverted digital function signal by one of said plural speed control signals, so that a resultant product comprises a function signal having a peak amplitude related to the magnitude of said one speed control signal,
• three commutation phase transistor driver means each being responsive to one analog phase driving signal, for applying a driving current to a phase winding of the brushless D.C. motor.