Struct DiffPairRoot 

pub struct DiffPairRoot {
    pub alpha: f64,
    pub n_vt: f64,
    pub i_tail: f64,
    pub i_tail_bias: f64,
    pub i_tail_max: f64,
    pub prev_v: f64,
}

Diff-pair macromodel for ladder filter stages (Moog/303/Korg).

Models one stage of a transistor ladder as a differential pair with tanh transfer characteristic:

I_out = α · I_tail · tanh(V_in / (2 · n · V_t))

where:

• α = β/(β+1) from SPICE BF parameter (collector current fraction)
• I_tail = tail current, modulated by cutoff CV (this IS the cutoff control)
• n = forward ideality factor (SPICE NF, usually ~1.0)
• V_t = thermal voltage (kT/q ≈ 25.85mV at 25°C)

The cap in the WDF tree is loaded by 1/gm = 2·n·Vt / (α·I_tail), giving cutoff frequency f_c = α·I_tail / (4π·n·Vt·C).

K-table: 2D lookup on (b_tree, I_tail). The I_tail axis maps to the cutoff control CV. Monotonic, bounded, memoryless — ideal for K-method.

Fields

alpha: f64

α = BF / (BF + 1), collector current fraction.

n_vt: f64

n · Vt: scaled thermal voltage (NF * kT/q).

i_tail: f64

Current tail current (modulated by cutoff CV).

i_tail_bias: f64

DC bias tail current (quiescent operating point).

i_tail_max: f64

Max tail current (sets cutoff range).

prev_v: f64

Previous sample’s voltage for NR warm-start.

Implementations

impl DiffPairRoot

pub fn from_gummel_poon( model: &GummelPoonModel, i_tail_bias: f64, ) -> DiffPairRoot

Create from SPICE Gummel-Poon parameters.

pub fn new(alpha: f64, n_vt: f64, i_tail: f64) -> DiffPairRoot

Create with explicit parameters.

pub fn set_i_tail(&mut self, i_tail: f64)

Set the tail current (cutoff control, audio rate).

pub fn i_tail_bias(&self) -> f64

Get the DC bias tail current.

pub fn gm(&self) -> f64

Transconductance gm = α · I_tail / (2 · n · Vt).

pub fn current(&self, v: f64) -> f64

Output current of the diff pair at voltage V. I = α · I_tail · tanh(V / (2 · n · Vt))

pub fn current_derivative(&self, v: f64) -> f64

Derivative dI/dV = α · I_tail / (2 · n · Vt) · sech²(V / (2·n·Vt))

pub fn process(&mut self, a: f64, rp: f64) -> f64

WDF NR solve: incident wave → reflected wave.

pub fn reset_nr_state(&mut self)

Reset NR warm-start state.

pub fn k_method_candidacy(&self) -> (bool, usize)

K-method candidacy: 2D (b_tree × I_tail).

Trait Implementations

impl Clone for DiffPairRoot

fn clone(&self) -> DiffPairRoot

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for DiffPairRoot

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl NlDeviceIv for DiffPairRoot

fn iv(&self, v: f64) -> (f64, f64)

Return (current, d_current/d_voltage) at the given port voltage.

fn v_clamp(&self) -> (f64, f64)

Return (v_min, v_max) voltage clamping bounds for this device.