
Rockbox mail archiveSubject: Re: Sanyo LV24020LP Coefficient "A" Constant CalculationRe: Sanyo LV24020LP Coefficient "A" Constant Calculation
From: Michael Sevakis <jethead71_at_sbcglobal.net>
Date: Sun, 11 Nov 2007 02:58:32 0500 There's nothing fancy to do. Just tell it the frequency you want to tune to and it will tune it within the driver. The endpoints of the curve are initialized by selecting each value of FM_OSC and FM_CAP at each extreme (four combinations) to find coefficients at four points. Therefter, any regsiter values are based upon an initial interpolation between the points and successive approximation until the measured frequency is within measurement tolerance. Usually it takes 14 cycles to achieve tuning. C=1/(L*4*pi^2) * 1/f^2 <= cap value for LC oscillator A=1/(L*4*pi^2) and is constant for any chip (tuning is done by changing C, not L). Which becomes: C=A/f^2 (f=+sqrt(A/C)) The function based on kHz is (and scaled for my convenience to saturate at a specific minimum f): static int calculate_coef(unsigned fkhz) { /* Overflow below 66000kHz  My tuner tunes down to a min of ~72600kHz but datasheet mentions 66000kHz as the minimum. ?? Perhaps 76000kHz was intended? */ return fkhz < 66000 ? 0x7fffffff : 0x81d1a47efc5cb700ull / ((uint64_t)fkhz*fkhz); } The extremes are used as curve endpoints here with no concern for the actual values and the coefficients for the points calculated based upon the measurements at tuner init. Thereafter, a coefficient is calculated for the desired frequency and that coeficient interpolated linearly between the measured endpoint coefficients to return the cap value to get that f. How much these chips actually vary in their available frequency range I don't know...I'm not even sure it's specified other than to say I saw 66000116000KHz there as the range needed without overflow. Nonetheless tuning to higher f won't overflow.  Original Message  From: "Brandon Irwin" <brandon.irwin_at_gmail.com> To: <rockbox_at_cool.haxx.se> Sent: Saturday, November 10, 2007 8:21 PM Subject: Sanyo LV24020LP Coefficient "A" Constant Calculation > Hello, > > In the LV24020Lp application note > http://www.rockbox.org/twiki/pub/Main/DataSheets/AN2400S04.pdf > tuning to a frequency relies on knowing a constant, A, that depends on > the inductor value for the tuner. > How was this value found/calculated for the lv24020lp.c driver? > > Brandon Irwin Received on 20071111 Page was last modified "Sat May 23 08:12:40 2020" The Rockbox Crew 