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I can not change peak to peak value of Vtune signal by using AD 9956.

Question asked by LGNS_ENGINEER40 on Aug 2, 2017
Latest reply on Aug 16, 2017 by mcee

Hi,

I want to sweep between 2100 and 2180 Mhz, 100 KHz intervals, 500 us period.
I use AD 9956 synthesizer for this. And my crystal is 25 MHz. 
I use the TM4C123GXL DSP as a microcontroller.

When I get a value of 500us, the required Vtune for Vco (CVCO55BE 2100-2200) should be between 2.00 and 3.50 volts, but I can not.
When I get 500us value, I can not make a change in peak to peak value.
Related code lines are below;

{
GPIOPinWrite(GPIO_PORTE_BASE, DDS3_ResetMaster, DDS3_ResetMaster);
GPIOPinWrite(GPIO_PORTE_BASE, DDS3_ResetMaster, ~DDS3_ResetMaster);

GPIOPinWrite(GPIO_PORTB_BASE, DDS3_Reset, DDS3_Reset);
GPIOPinWrite(GPIO_PORTB_BASE, DDS3_Reset, ~DDS3_Reset);

GPIOPinWrite(GPIO_PORTE_BASE, DDS3_PS0, ~DDS3_PS0);

GPIOPinWrite(GPIO_PORTE_BASE, DDS3_Update, ~DDS3_Update);

write5byte(0x00,0x00,0x02,0x40,0x20); //Linear sweep no dwell
write6byte(0x01,0x01,0x02,0x78,0x00,0x07); //write cfr2
//rising
write4byte(0x02,0x00,0x18,0x80); // 100 KHZ
write3byte(0x04,0x00,0x07); // 0.1 us
//falling
write4byte(0x03,0x00,0x18,0x80); // 100KHz
write3byte(0x05,0x00,0x07); // 0.1us
// fwto
write9byte(0x06,0x00,0x00,0x14,0x18,0xE1,0xDA,0xAD,0x38); // 21 MHz
// fwto
write9byte(0x07,0x00,0x00,0x19,0x5C,0x59,0xF5,0x79,0x10); // 26.5 MHz
}

while(1)
{
GPIOPinWrite(GPIO_PORTE_BASE, DDS3_PS0, DDS3_PS0);
SysCtlDelay(26666666/12000);
GPIOPinWrite(GPIO_PORTE_BASE, DDS3_PS0, ~DDS3_PS0);
SysCtlDelay(26666666/12000);
}

Outcomes