Z90251 Datasheet, PDF (87/97 Pages) Zilog, Inc. – eZVision 200 Television Controllers with OSD

Z90255 ROM and Z90251 OTP
32 KB Television Controller with OSD
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9.3 Digital/Analog Conversion with PWM
The televison OSD controller can generate square waves which have fixed
periods but variable duty cycles. If this type of signal passes through an RC
integrator, the output is a DC voltage proportional to the pulse width of the square
wave. Refer to Figure 20, Cases A and B show fixed voltage samples while Case
C shows a varying voltage example.
PWM Signal
DC Signal
Case A
PWM Signal
Case B
PWM Signal
Case C
V_CC Voltage
DC Signal ^Time
V_CC ^Voltage
DC Signal ^Time
V_CC ^Voltage
PWM Signal
DC Signal
Time
Figure 20 Analog Signals Generated from PWM Signals
PS001301-0800