GMZAN3 Datasheet, PDF (20/53 Pages) List of Unclassifed Manufacturers – XGA ALALOG INTERFACE LCD MONITOR CONTROLLER

gmZAN3 Preliminary Data Sheet
a wide range of conditions. The oscillator circuit also minimizes the overdrive of the crystal, which
reduces the aging of the crystal.
When the gmZAN3 is in reset, the state of the HDATA2/AD2/OSC_SEL pin is sampled. If the pin is
pulled high by connecting to VDD through a pull-up resistor (10KΩ recommended, 15KΩ maximum)
then internal oscillator is enabled. In this mode a crystal resonator is connected between TCLK and the
XTAL with the appropriately sized loading capacitors C_L1 and C_L2. The size of C_L1 and C_L2 are
determined from the crystal manufacturer’s specification and by compensating for the parasitic
capacitance of the gmZAN3 device and the printed circuit board traces. The loading capacitors are
terminated to the analog VDD power supply. This connection increases the power supply rejection ratio
when compared to terminating the loading capacitors to ground.
Vdda
CL1
111
TCLK
Vdda
110
XTAL
CL2
Vdda
10 K
126
HDATA2/AD2/OSC_SEL
gmZAN3
Vdd
100 K
180 uA
Internal Pull Down
Resistor
~ 60K
Reset State Logic
OSC_OUT
TCLK Distribution
Internal Oscillator Enable
Figure 5.
Using the Internal Oscillator with External Crystal
The TCLK oscillator uses a Pierce Oscillator circuit. The output of the oscillator circuit, measured at the
TCLK pin, is an approximate sine wave with a bias of about 2 volts above ground (see Figure 6). The
peak-to-peak voltage of the output can range from 250 mV to 1000 mV depending on the specific
characteristics of the crystal and variation in the oscillator characteristics. The output of the oscillator is
connected to a comparator that converts the sine wave to a square wave. The comparator requires a
C0523-DAT-01G
20
Genesis Microchip Confidential
http://www.genesis-microchip.com
July 2003