lockin: add rounding bias
@@ -16,6 +16,7 @@ impl Lockin {
}
/// Update the lockin with a sample taken at a given phase.
+ /// The lowpass has a gain of `1 << k`.
pub fn update(&mut self, sample: i16, phase: i32, k: u8) -> Complex<i32> {
// Get the LO signal for demodulation.
let lo = Complex::from_angle(phase);
@@ -23,8 +24,10 @@ impl Lockin {
// Mix with the LO signal, filter with the IIR lowpass,
// return IQ (in-phase and quadrature) data.
Complex(
- self.state[0].update((sample as i32 * (lo.0 >> 16)) >> 16, k),
- self.state[1].update((sample as i32 * (lo.1 >> 16)) >> 16, k),
+ self.state[0]
+ .update((sample as i32 * (lo.0 >> 16) + (1 << 15)) >> 16, k),
+ self.state[1]
+ .update((sample as i32 * (lo.1 >> 16) + (1 << 15)) >> 16, k),
)
}
}
