Nice page really taking shape On Fri, Jan 27, 2012 at 1:27 PM, beale <[email protected]> wrote:
> I added a bit to the "electronics" section of the FE-5680A FAQ as below. > > http://www.ko4bb.com/dokuwiki/doku.php?id=precision_timing:fe5680a_faq#electronic > > (Note- until today, I had the 8 and 6 digits transposed, calling it the > fe5860a. But no one noticed :-) > > The updated section is below. I measured the 20 MHz input and 5.3 MHz > output of the DDS, but I'm puzzled by how the tuning resolution (4.6 mHz) > of the DDS output is divided by such a large factor to achieve 0.18 uHz > resolution at the final 10 MHz output. Can any frequency synthesizer gurus > explain how this is done? > > ----------------------------- > The main digital electronic parts are: > > Maxim DS80C323END (8051, 44TQFP, -40/+85C, 18 MHz, 4 8-bit ports, > 64K/64K ROM/RAM ) > STMicro PSD813F1V-20UI (1Mbit flash, 256Kbit EEPROM, 16Kbit SRAM, 3k > PLD gates, ISP) > Xilinx XC9572XL VQ64BN (64-pin CPLD, 178 MHz, 72 macrocells) > Analog Devices AD9832BRU (25 MHz Direct Digital Synthesizer, on-chip > 10-bit DAC) > > Other ICs on digital side of PCB: > > Maxim MAX708 CPU supervisor > Maxim DS1832 CPU watchdog, brownout detect > Maxim MAX882 3.3V LDO (5V input) > Maxim MAX1246 4 ch. 12-bit ADC > Maxim MAX3232 RS-232 transciever > > Operation > > A 60 MHz sine from the VCXO enters CPLD pin 64 and it generates 3.3V > square wave outputs at 30 MHz (pin 22), 20 MHz (pin 1), and 10 MHz (pin > 49). The 20 MHz output goes to the clock input of the AD9832 DDS chip, > which generates a 5.3 MHz sinewave output (nominal, when the RS-232 offset > is set to 0). The frequency resolution of the DDS itself is (Fclock)/2^32 > and since Fclock=20 MHz, the 5.3 MHz output is tuned in steps of 4.657E-3 > Hz. However, the FE-5860A 10 MHz output step size is 1.7854E-7 Hz, so the > DDS output frequency must be effectively divided in the overall system by a > factor of about 26000 at the 10 MHz output (or a factor of 4333 at the 60 > MHz VCXO frequency). The Rb hyperfine transition is at 6.835 GHz which is > about 683x larger than 10 MHz. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
