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Why is the use of different PLL feedback modes in Altera devices?

Altera_Forum
Honored Contributor II
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The documentation states that the Altera PLLs have 6 different clock feedback modes. These are:  

 

1. Direct mode 

2. Normal mode 

3. Source-Synchronous mode 

4. External Feedback mode 

5. Zero-Delay Buffer mode 

6. LVDS mode 

 

 

Why are there so many clock feedback modes and how do I know which one I need?
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Altera_Forum
Honored Contributor II
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--- Quote Start ---  

The documentation states that the Altera PLLs have 6 different clock feedback modes. These are:  

 

1. Direct mode 

2. Normal mode 

3. Source-Synchronous mode 

4. External Feedback mode 

5. Zero-Delay Buffer mode 

6. LVDS mode 

 

 

Why are there so many clock feedback modes and how do I know which one I need? 

--- Quote End ---  

 

 

They are offered to tackle timing problems in case you have io violations. 

Direct : only de-jitters clock, does not compensate for delay. 

normal, de-jitters and reduces clock delay from pin to register and compensates for clock delay from pin 

source synchronous, keeps data/clk phase same between pins and registers 

external: relevant if so 

zero delay: relevant to an output clock from pll, maintains same phase of output clock as that of input clock. 

lvds: relevant to serdes.
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Altera_Forum
Honored Contributor II
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if I am connecting a audio DAC that needs MCLK (master clock) and takes I2S signals SCLK, Data and LRCK (same frequency as audio sample rate, used to select left/right channels), and I intend to generate MCLK and other clock signals from a PLL inside the FPGA, which of these shall I need to use?

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