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feat(max2871): First mixer_set_frequency implementation

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This commit is contained in:
Tobias Schneider
2015-06-08 00:54:56 +02:00
parent c79c53c52f
commit e7dedb761e
1 changed files with 10 additions and 117 deletions
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127
firmware/common/max2871.c
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@ -21,122 +21,6 @@ static void max2871_spi_write(uint8_t r, uint32_t v);
static void max2871_write_registers(void);
static void delay_ms(int ms);
/*
* - The input is fixed to 50 MHz
* f_REF = 50 MHz
*
* - The VCO must operate between 3 GHz and 6 GHz
* f_VCO range: 3 GHz - 6 GHz
*
* Phase Detector Clock:
* - We configure the phase detector to not change the
* input signal
* f_PFD = f_REF x [(1 + DBR)/(R x (1 + RDIV2))]
* R = 1
* DBR = 0
* RDIV2 = 0
*
* => f_PFD = 50 MHz
*
*
* f_RFOUT < 3 GHz:
* - To go to < 3 GHz, f_VCO has to be divided.
* f_RFOUT = f_VCO / DIVA
*
* - We just divide by 2 for now
* DIVA = 2
* => f_RFOUT = f_VCO / 2
*
* - Relationship between f_PFD (fixed) and f_VCO (variable)
* N + (F/M) = f_VCO/ f_PFD
*
* - Insert relationship between f_RFOUT and f_VCO:
* N + (F/M) = (f_RFOUT * 2) / f_PFD
* f_RFOUT = (N + F/M) * f_PFD / 2
*
* - Limits for N, M and F from the datasheet:
* 19 <= N <= 4091
* 2 <= M <= 4095
* F < M
*
* - Plug in constants:
* f_RFOUT = (N + F/M) / 2 * 50 MHz
*
* - Given the range of N, we can go to:
* f_RFOUT range: 475 MHz - 3 GHz
*
* - N steps in 25 MHz increments:
* N = floor(f_RFOUT / 50 MHz * 2)
* => N = (f_RFOUT * 2) / 50 MHz (uses integer math)
*
* - Calculate the error:
* f_int_ERROR = f_RFOUT - (N * 50 MHz) / 2
* f_int_ERROR range: 0 MHz - 24 MHz
*
* - Use the fraction to get to the correct frequency:
* (F/M) / 2 * 50 MHz = f_int_ERROR
*
* - Fix M:
* M = 25
*
* - Calculate F:
* (F/25) / 2 * 50 MHz = f_int_ERROR
* F = f_int_ERROR / 1 MHz
*
* - Calculate the new error:
*
* f_ERROR = f_RFOUT - (N + F/M) / 2 * 50 MHz
* f_ERROR range: 0 MHz - 1 MHz
*
*
* f_RFOUT > 3 GHz:
* - Do not divide the VCO output
* DIVA = 1
* => f_RFOUT = f_VCO
*
* - Relationship between f_PFD (fixed) and f_VCO (variable)
* N + (F/M) = f_VCO/ f_PFD
*
* - Insert relationship between f_RFOUT and f_VCO:
* N + (F/M) = f_RFOUT / f_PFD
* f_RFOUT = (N + F/M) * f_PFD
*
* - Limits for N, M and F from the datasheet:
* 19 <= N <= 4091
* 2 <= M <= 4095
* F < M
*
* - Plug in constants:
* f_RFOUT = (N + F/M) * 50 MHz
*
* - Given the range of N and the VCO limits, we can go to:
* f_RFOUT range: 3000 MHz - 6000 MHz
*
* - N steps in 50 MHz increments:
* N = floor(f_RFOUT / 50 MHz)
* => N = f_RFOUT / 50 MHz (uses integer math)
*
* - Calculate the error:
* f_int_ERROR = f_RFOUT - N * 50 MHz
* f_int_ERROR range: 0 MHz - 49 MHz
*
* - Use the fraction to get to the correct frequency:
* (F/M) * 50 MHz = f_int_ERROR
*
* - Fix M:
* M = 50
*
* - Calculate F:
* (F/50) * 50 MHz = f_int_ERROR
* F = f_int_ERROR / 1 MHz
*
* - Calculate the new error:
*
* f_ERROR = f_RFOUT - (N + F/M) * 50 MHz
* f_ERROR range: 0 MHz - 1 MHz
*
*/
void mixer_setup(void)
{
/* Configure GPIO pins. */
@ -291,7 +175,16 @@ static void max2871_write_registers(void)
/* Set frequency (MHz). */
uint64_t mixer_set_frequency(uint16_t mhz)
{
(void) mhz;
int n = mhz;
int diva = 0;
while(n < 3000) {
n *= 2;
diva += 1;
}
max2871_set_N(n);
max2871_set_DIVA(diva);
return mhz;
}