RadioProcessor
Clock Input Signal Standard
It is also possible to use an external 50 MHz clock source to drive the RadioProcessor board, but
this
should be done with extreme caution
. The RadioProcessor is a digital system built in CMOS technology
and powered off a 3.3 V DC source and will accept external clock signals that conform to the low-voltage 3.3 V
TTL standard only. Negative voltage below 0.2 Volts would damage the processor chip, and thus
any
external sinusoidal signal would need to be converted to the positive-only TTL signal prior to using
with the RadioProcessor.
Alternative Sampling Frequencies
The RadioProcessor can be customized to operate with alternative sampling frequencies. An example
alternative A/D sampling frequency value also suitable for 70 MHz IF applications (demonstrated in Appendix
I) would be 60 MHz. At this frequency, the 70 MHz input signal would fold, when sampled, into the apparent
10 MHz frequency. This apparent 10 MHz signal would be handled by the RadioProcessor's digital detection
and filtering system in the same way as any other signal within the Nyquist range. To operate in the coherent
mode at 60 Ms/s, the RadioProcessor master clock source would need to be 40 MHz. With the reference
clock frequency of 40 MHz, the Tx DAC would operate at 240 MHz.
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/
/RadioProcessor “On the Fly” register programming.
/
/Note: It is assumed that there is a Pulse Program already running using
frequency register 0.
int main()
{
if
(pb_init())
{
printf ("Error initializing board: %s\n",
pb_get_error());
return -1;
}
pb_core_clock(75.0);
i
nt
i;
for
( i=0 ; i <10 ; i++ )
{
pb_start_programming(FREQ_REGS);
pb_set_freq( ( ( (double)i )+1.0)*MHz);
pb_stop_programming();
pb_sleep_ms(1000);
//Wait 1 second.
}
pb_close();
return 0;
}
Example A5.2:
Using SpinAPI to perform a frequency sweep from 1 to 10 MHz using
frequency register zero. The frequency is incremented once every 1000 ms.
www.spincore.com
