GM5120 データシートの表示（PDF） - Genesis Microchip

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GM5120

XGA/SXGA LCD Controller

Genesis Microchip 

*** Genesis Microchip Confidential ***

gm5110/20 Preliminary Data Sheet

The gm5110/20 TCLK oscillator circuitry is a custom designed circuit to support the use of

an external oscillator or a crystal resonator to generate a reference frequency source for the

gm5110/20 device.

4.1.1 Using the Internal Oscillator with External Crystal

The first option for providing a clock reference is to use the internal oscillator with an

external crystal. The oscillator circuit is designed to provide a very low jitter and very low

harmonic clock to the internal circuitry of the gm5110/20. An Automatic Gain Control

(AGC) is used to insure startup and operation over a wide range of conditions. The oscillator

circuit also minimizes the overdrive of the crystal, which reduces the aging of the crystal.

When the gm5110/20 is in reset, the state of the ROM_ADDR13 pin (pin number 10) is

sampled. If the pin is left unconnected (internal pull-down) then internal oscillator is enabled.

In this mode a crystal resonator is connected between TCLK (pin 152) and the XTAL (pin

151) with the appropriately sized loading capacitors CL1 and CL2. The size of CL1 and CL2 are

determined from the crystal manufacturer’s specification and by compensating for the

parasitic capacitance of the gm5110/20 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

152

TCLK

Vdda

CL2

151

XTAL

gm5115

Vdd

100 K

180 uA

OSC_OUT

TCLK Distribution

10

N/C

ROM_ADDR13

Internal Pull Down

Resistor

~ 60K

Reset State Logic

Internal Oscillator Enable

Figure 4.

Using the Internal Oscillator with External Crystal

June 2002

11

C5110-DAT-01C

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