Frequency Generator
for
Spartan-3E Starter Kit
Ken Chapman
Xilinx Ltd
18
th
July 2006
Rev.1
With special thanks to
Peter Alfke and Alireza Kaviani.
Страница 1: ...Frequency Generator for Spartan 3E Starter Kit Ken Chapman Xilinx Ltd 18th July 2006 Rev 1 With special thanks to Peter Alfke and Alireza Kaviani ...
Страница 2: ...liable for any loss of data lost profits cost or procurement of substitute goods or services or for any special incidental consequential or indirect damages arising from the use or operation of the designs or accompanying documentation however caused and on any theory of liability This limitation will apply even if Xilinx has been advised of the possibility of such damage This limitation shall app...
Страница 3: ...e to the hardware which means that you can use this design with your board to determine the exact values required to implement a fixed frequency synthesizer without requiring PicoBlaze the knob and LCD display On this board the technique provides a convenient alternative to fitting a special oscillator in the IC16 socket and it may proves a cost effective solution for many real product application...
Страница 4: ...ack line under the digit in the top line Edit digit value mode Press and release knob to toggle between frequency editing modes Edit cursor position mode In this mode rotating the knob to the left or right will decrement or increment the value of the digit located at the cursor position The controller will automatically borrow from or carry to the more significant digits to the left of the digit b...
Страница 5: ...d frequency version Number of occupied Slices 172 out of 4 656 3 Number of Block RAMs 1 out of 20 5 DCMs 2 out of 4 50 Total equivalent gate count for design 91 537 PicoBlaze makes extensive use of the distributed memory features of the Spartan 3E device leading to very high design efficiency If this design was replicated to fill the XC3S500E device it would represent the equivalent of over 1 5 mi...
Страница 6: ... included with the reference design as it is provided with PicoBlaze download Please visit the PicoBlaze Web site for your free copy of PicoBlaze assembler JTAG_loader and documentation www xilinx com picoblaze Hint The JTAG_Loader utility supplied with PicoBlaze has been included in this design This enables the new programs to be written for PicoBlaze using the configuration file provided This de...
Страница 7: ...decimal so the output from the phase accumulator is 9 5MHz a period of approximately 105ns That means that the accumulator synthesizes one output cycle for approximately 21 cycles of the 200MHz clock from which the accumulator runs CLKIN BUFG frequency_aligned_dcm DCM CLKFX CLKFX_MULTIPLY 256 CLKFX_DIVIDE 16 dcm_clean_clk synth_clk The second DCM is used in a frequency aligned mode At the time of ...
Страница 8: ...4 led 3 led 2 led 1 led 0 led 7 output_ports rotary_a rotary_press rotary_b lcd_rs lcd_e lcd_rw lcd 7 6 lcd 6 lcd 5 lcd 4 lcd 7 lcd 6 lcd 5 lcd 4 bidirectional LCD data rotary_press_in See reference design called Rotary Encoder Interface for Spartan 3E Starter Kit for details of this section rotary_event rotary_left rotary_filter direction clk 50MHz clock to all items on this page 2 3 4 5 1 dds_sc...
Страница 9: ...8 cycles 200MHz 8 cycles 200MHz This waveform shows what happens when you try to synthesize a 12 4125MHz clock using the phase accumulator There is clearly 5ns of cycle to cycle jitter in this situation because each output cycle really should be formed of 16 113 periods of the 200MHz clock which is impossible Therefore what the phase accumulator is doing is to provide the correct average frequency...
Страница 10: ...synthesis process and this is reflected by a distinct 12 5MHz component which is 45dB above the noise floor The zoomed plot shows how the fundamental covers only a narrow bandwidth keeping in mind that the resolution of the FFT is only 50KHz Note the third harmonic of a square wave is also very distinct at 37 5MHz and is even close to being the theoretical 9 54dB down from the fundamental 1 3 ampl...
Страница 11: ...d mode you must accept that it does NOT maintain phase lock as it does in all other normal modes More significantly the output frequency is the average of the input frequency which means there will often be a slight difference as it tracks the input You may have to look closely to notice that this second plot really is 12 4125MHz It is immediately clear that there is no obvious cycle to cycle jitt...
Страница 12: ...stay balanced because we are unable to freeze completely due to other influences on us and the need to breath etc 12 5MHz Fundamental 5MHz division 10dB division 1MHz division 10dB division 3rd Harmonic 12 5MHz Fundamental 12 4125MHz Fundamental 12 4125MHz Fundamental The full spectrum of the 12 4125MHz case shows how the previous family of spectral components associated with the 5ns of cycle jitt...
Страница 13: ...amming File Then right click and select Properties to open the Process Properties box 2 The Process Properties box should open with the General Options being shown otherwise select General Options on the left Move to the line Other Bitgen Command Line Options and enter the text string shown below 3 Select Apply and then use OK to exit the box Hint Reopen the box and confirm the option really was s...
Страница 14: ...h frequencies you require then reduce the design to a phase accumulator driven by a constant N the DCMs and a fixed counter divider no multiplexer Hint If you still operate the phase accumulator at 200MHz then use the supplied design on the board to calculate your N and D values for you Hint Remember to share the 200MHz fast clock between several phase accumulators to save DCMs Accurate Measuremen...
