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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| 3 phase , frequency agile, ULTRA high purity sine generator |
 Posted: Sun Feb 22, 2015 5:44 pm |
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This code generates a 3 phase high purity ( harmonics ~-60dBsc),
or arbitrary phase sine wave locked to better than 250nsec absolute phase.
The AD9833 NCO is the target chip and uses just 5 lines on a single PIC port
or addressable latch. There are 3 chips in total - one for each phase - with clock and load/shift common to all 3.
There is separate data for a,b and c chips .
Phase is set to one part in 4096 of 360 degrees by altering the vars:
phaseA, phaseB, phaseC, before a call to change frequency.
Better than one hz resolution is available using an 8.388 mhz input to the
AD 9833 chip clock, for output frequencies below 512khz with rock solid amplitude and vanishingly low distortion.
a single master oscillator is required to feed all three NCO's...
| Code: |
//
// to alter oscillator phase on the fly- change phase (a) (b)(c) values and call
// DNO_FREQSET_LL();
//
// this does basic init of oscillator trio of AD9833 NCO 10 bit sine
// wave generators clocked at 8388608 hz
//
//
// |---A (REF) data B2
// ||--B OSC B3
// |||-C OSC B4
// ||||-- 9833 CLOCK to all 3 chips B1
// |||||----not load/shift B0
// |||||
byte oscl 0b00000011; // b port phantom control var
unsigned int32 infreq=0; // master frequency
// global phase angle values follow
unsigned int16 phasea=0,phaseb=1365,phasec=2731; // 120 degree
// unsigned int16 phasea=0,phaseb=1023,phasec=3072; // dual quadrature
unsigned int16 lopart=0x1000; // actual divisors w/o added 4000 hex
unsigned int16 hipart=0x1f; // for 16 khz default frequency at INIT
unsigned int32 outdiv=0;
#define DL8 delay_cycles(8)
// above delay for 64 mhz clock used in 18f46k22 test PIC
// ------------------
// phase adjusting driver
// flag==0 means use individual phase words ,flag==1 set all to 'Q'
// ------------------
//
VOID DNOdrVP(int1 flag , unsigned int16 Q){
unsigned INT8 I=0;
unsigned int16 MPA=0b1100000000000000;
unsigned int16 MPB=0b1100000000000000;
unsigned int16 MPC=0b1100000000000000;
#BIT OBIT=Q.15
#bit PHSA=MPA.15
#bit PHSB=MPB.15
#bit PHSC=MPC.15
if(0==flag){
MPA |=phasea; MPB |=phaseb; MPC |=phasec;
}
else{
MPA |=Q; MPB |=Q; MPC |=Q; // note Q for all phases
}
oscl |=0b00010011; // raise clock &loadshift
output_b(oscl);
DL8; //
output_low(pin_b0);
do{ // do both a and b data
if (PHSA) output_high(pin_b2); // oscl |=0b00000111;
else output_low(pin_B2); // oscl &=0b11111011;
if (PHSb) output_high(pin_b3); //oscl |=0b00001011;
else output_low(pin_B3 ); // oscl &=0b11110111;
if (PHSC) output_high(pin_b4); //oscl |=0b00001011;
else output_low(pin_B4 ); // oscl &=0b11110111;
output_low(pin_b1); // low clock
DL8;
output_high(pin_b1); // raise then shift bits
MPA <<=1; MPB <<=1; MPC <<=1;
I++;
}WHILE (I<16);
output_low(pin_B2); output_low(pin_B3); output_low(pin_B4);
DL8;
output_high(pin_b0);
oscl |=0b00010011; // RAISE loadshift
output_B(oscl); //
}
// frequency changer
VOID DNOdrV(unsigned int16 Q){
#BIT OBIT=Q.15
unsigned INT8 I=0;
oscl |=0b00010011; // raise clock &loadshift
output_B(oscl);
DL8;
output_low(pin_b0);
DL8;
do{ // do both a and b data
if (OBIT) { output_high(pin_B2); output_high(pin_B3);output_high(pin_B4);}
else { output_low(pin_B2); output_low(pin_B3); output_low(pin_B4);}
DL8;
output_low(pin_b1); // low clock
DL8; ///delay_cycles(8);
output_high(pin_b1); // raise
DL8; ///delay_cycles(8);
Q <<=1; //shift bits
I++;
}WHILE (I<16);
output_low(pin_B2); output_low(pin_B3);
DL8; output_high(pin_b0);
oscl |=0b00010011; // RAISE loadshift
output_B(oscl); //
}
void LLfreq (void){
DNOdrvP(0,0); delay_us(4);
DNOdrv( (0x4000+lopart )); delay_us(4);
DNOdrv( (0x4000+hipart ));
}
void DNO_FREQSET_LL(void ){
hipart= (infreq >> 9); lopart= ((infreq<<5)&16383 ); //
LLfreq();
}
//
// DNO_mode: ALWAYS sine wave for this app
// CALL THIS BEFORE ANY OTHER CALL to PREP/INIT
// the 9833's or reset them
void setupDNO(void ){ // mode
// setup this resets the chip to a ready state
DNOdrv(0x2100); // send RESET SIN word case 0 and 1 for now
delay_US ( 10 );
llfreq();
DNOdrvP(1,0xC000); // PHASE CTL word to mid scale
// send the two block prep word for curr mode
DNOdrv(0x2000); // send RESET SIN word case 0 and 1 for now
delay_US ( 10 ); // dp 911 was 4 us add delay
llfreq();
}
// change all 3 NCO sine frequencies with this call
// while maintaining accurate phase relationships
// update phase a,b,c by altering the values of each var
// before calling this master function
//** 'option' is the INTEGER frequency you want to set
void dnofreqset( unsigned int32 option ){
infreq=option; DNO_FREQSET_LL();
} |
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freedom
Joined: 10 Jul 2011
Posts: 54
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| Posted: Thu Nov 26, 2015 9:00 am |
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Thanks a lot asmboy for posting 3 phase , frequency agile, ULTRA high purity sine generator
1. What do you mean by NCO (ref: AD9833 NCO) ?
| Quote: | | " Phase is set to one part in 4096 of 360 degrees by altering the vars: " |
2. Please explain the above statement.
3. Can this code can be used for 3 phase AC motor inverter ?
4. Would you like to post an example circuit ?
thanks |
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asmboy
Joined: 20 Nov 2007
Posts: 2128
Location: albany ny
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| Posted: Thu Nov 26, 2015 10:52 am |
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1. NCO = Numerically controlled oscillator aka DNO Digital numeric Oscillator.
The mfgr: calls their version of the technology
DDS -Direct Digital Synthesis
Their description says
The AD9833 is a low power, programmable waveform generator
capable of producing sine, triangular, and square wave outputs.
Call it whatever you like ;-))
2. From the AD9833 datasheet - the phase control word is 12bits -
and the vars are phasea,b,c --- got it ?
3. YES - IF you have a suitable power amplifier circuit.
// This circuit has MUCH lower harmonic content than the usual source for a power inverter however.
4. circuit for what ?
This design was created for a multi-channel synchronous demodulator.
basic circuit examples are in the AD datasheet. This allows a reference channel and 'X' and 'Y' with quadrature or any other phase relationships you desire -plus phase offsets in 12 bit space. |
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