GM5120H 查看數據表（PDF） - Genesis Microchip

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GM5120H

XGA/SXGA LCD Controller

Genesis Microchip 

*** Genesis Microchip Confidential ***

gm5110/20 Preliminary Data Sheet

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 5). 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 minimum signal level of

about 50-mV peak to peak to function correctly. The output of the comparator is buffered and

then distributed to the gm5110/20 circuits.

3.3 Volts

~ 2 Volts

250 mV peak to peak

to

1000 mV peak to peak

Figure 5.

time

Internal Oscillator Output

One of the design parameters that must be given some consideration is the value of the

loading capacitors used with the crystal as shown in Figure 6. The loading capacitance (Cload)

on the crystal is the combination of CL1 and CL2 and is calculated by Cload = ((CL1 * CL2) /

(CL1 + CL2)) + Cshunt. The shunt capacitance Cshunt is the effective capacitance between the

XTAL and TCLK pins. For the gm5110/20 this is approximately 9 pF. CL1 and CL2 are a

parallel combination of the external loading capacitors (Cex), the PCB board capacitance

(Cpcb), the pin capacitance (Cpin), the pad capacitance (Cpad), and the ESD protection

capacitance (Cesd). The capacitances are symmetrical so that CL1 = CL2 = Cex + CPCB + Cpin +

Cpad + CESD. The correct value of Cex must be calculated based on the values of the load

capacitances. Approximate values are provided in Figure 6.

June 2002

12

C5110-DAT-01C

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