Given the PWM D/A performance parameters previously discussed, users might wonder what range of frequencies can be produced. Remember that according to the Nyquist criteria, customers must output samples at a rate at least twice that of the highest frequency they wish to generate. Moreover, a higher sample rate is better. With this restriction in mind, if a full 14-bit PWM D/A conversion is used at 10MHz, the maximum frequency that can be produced is one half of the conversion time. If the conversion time is 1638.4µs, the highest output frequency is 305.17Hz. If the resolution is lowered to 10-bits, the conversion time drops to 102.4µs. This allows the D/A to produce a maximum output frequency of 4882.81Hz. These design examples show that a user can tune a system to meet a range of frequency and accuracy requirements. They also reveal that the maximum output frequencies the PWM D/A can produce are relatively low compared to a standard R-2R D/A. Admittedly, though, that type of converter typically offers only 8-bit resolution.