Implementation in hardware
Since October 2001, new digital output types have been available for the cards of the Multichoice PCI series. The previously available pulse-width modulated output has been completely revised, earlier dropouts when writing a new pulse-pause ratio are a thing of the past. The PWM and FM switching mimics are implemented in the FPGA of the measurement card, so that this module takes over the controls in hardware, so to speak. This solution enables higher update speeds and better stability of the output without taking up computing time of the signal processor.

Completely new possibilities
With some drivers, pulse width modulation and frequency modulation are even available at the same time, so that pulse width and frequency can be modified in parallel in a circuit diagram during runtime. This parallel modification enables completely new solutions for previous problems such as valve controls or test stands.

Better resolution In
addition, a second variant of the pulse-width modulated output was developed which, instead of the previous 16-bit depth with a clock rate of 500 kHz, has a depth of 24 bits and a clock rate of 10 MHz. This significantly increased the accuracy of the PWM output. Furthermore, the frequency spectrum now ranges from 0.6 Hz to 5 MHz.

Frequency modulation as a free bonus
The third innovation was frequency modulation. This behaves like a pulse-width-modulated output with a variable frequency and a specified mark-to-space ratio.

The PWM modulates the pulse width of a square wave signal with a constant period. The pulse width is given as a percentage of the period. If the pulse width is 0%, the PWM output is always low. If it is 100%, the output is always high. At 50%, the low and high levels are the same length.

Pulse width signal with a) 0%, b) 25%, c) 50%, d) 75% and e) 100%

Frequency modulation (FM)

With FM, the period of a square wave signal is modulated. The duty cycle remains constant. The smallest possible period is the maximum possible frequency and the largest possible period is the minimum possible frequency.