Capacitance meter using a DC bias that ramps up and a sinusoidal signal source, with current sensing on return leg.

Use this to measure capacitance of an active circuit, e.g., MOSFET ciss, coss, and crss.

Construct and use only via the mc_addedBias or mc_separateBias class method.

The subcircuit has six external subcircuit nodes:

npos: The positive node at which AC (and possibly also DC bias) current emerges to the device under test.
nneg: The negative node for return of the test current.
bias: A positive node for DC bias output, ground referenced.
cap: Output with voltage representing the calculated capacitance in Farads.
filt_in: Input of an RC lowpass filter with the same S-response as the one used in the RMS current calculation. In most cases, you will short this to bias.
filt_out: Output of the RC lowpass filter. Use observations of this for the independent vector in dynamically measured capacitance setups.
xl: Input with voltage representing the series inductance in Henries. Makes capacitance calculation more accurate if series inductance is at least partially known.

Parameters	fa	The AC signal frequency. (type: float)
	Na	Number of AC signal cycles in the bias sweep. (type: int)
	Nd	Number of AC signal cycles to delay before starting the bias sweep. (type: int)
	Vac	The AC signal voltage (peak-to-peak). (type: float)
	Vdc	A 2-sequence with (1) the starting and (2) ending DC bias voltage.
	bias_add	Set `True` to have the DC bias voltage added to the AC signal at npos. It will appear by itself, with no AC component, at the bias terminal regardless. Default: `False`. (type: bool)
	Ls	If at least some of the series inductance is known, set this to it to make the capacitance calculation more accurate. AV compatible. Default: 0 Henries.
	invert_bias	Set `True` to invert the voltage applied as bias, for P-channel MOSFETs. The bias output remains positive. (type: bool)

Class Method	correct	Returns an approximate correction factor to account for high capacitance readings due to imperfect sampling of the AC test signal.
Class Method	mc_addedBias	Makes an instance of me with bias added to the AC test signal and sent through the matching filter, and connects it to the specified nodes.
Class Method	mc_separateBias	Makes an instance of me with a separate bias output (also sent through the matching filter) and connects it to the specified nodes.
Method	sources	Undocumented
Method	lpf	Makes a lowpass filter following the cosine product and for the matched copy between filt_in and filt_out.
Method	v_x	Makes a voltage source v_x with the calculated reactance (90-degree current flow vs voltage), based on current through zero-voltage source Vsh.
Method	v_capacitance	Makes a voltage source cap with calculated capacitance, based on squared impedance indicated at node z2 and known series resistance and inductance.
Method	setup	Subcircuit definition.
Class Method	_xl	Called by `mc_addedBias` and `mc_separateBias` to make voltage source cmv_xl.

Inherited from NodeStuff (via Subcircuit):

Instance Variable	shunts	A dict of current sensing V elements with the pairs of nodes they connect.
Class Variable	debug	A `Bag` that gets set `True` for all instances to log info about each `setup` call.
Class Method	autoName	Undocumented
Method	setupResults	Undocumented
Method	fill	Undocumented
Method	nodeCheck	Call with the circuit building tool f and a sequence of nodes provided to this `Include` or `Subcircuit`.
Method	rawNetlist	Get lines of a raw netlist from a search hierarchy of possible sources.
Method	shunt	Call to insert a current-measuring shunt and add an entry to my `Elements` baton's dict of shunts.
Method	raw	See `Elements.raw`.
Method	iNode	See `Elements.iNode`.
Method	ground	See `Elements.ground`.
Method	sca	See `Elements.sca`.
Method	sca6	See `Elements.sca6`.
Class Method	_libDir	Undocumented
Method	_strippedLines	Undocumented
Method	_call_setup	Calls my `setup` method (almost always your override of that method, actually) and processes any return value.

Inherited from NodeStuff (via Subcircuit):

Instance Variable	shunts	A dict of current sensing V elements with the pairs of nodes they connect.
Class Variable	debug	A `Bag` that gets set `True` for all instances to log info about each `setup` call.
Class Method	autoName	Undocumented
Method	setupResults	Undocumented
Method	fill	Undocumented
Method	nodeCheck	Call with the circuit building tool f and a sequence of nodes provided to this `Include` or `Subcircuit`.
Method	rawNetlist	Get lines of a raw netlist from a search hierarchy of possible sources.
Method	shunt	Call to insert a current-measuring shunt and add an entry to my `Elements` baton's dict of shunts.
Method	raw	See `Elements.raw`.
Method	iNode	See `Elements.iNode`.
Method	ground	See `Elements.ground`.
Method	sca	See `Elements.sca`.
Method	sca6	See `Elements.sca6`.
Class Method	_libDir	Undocumented
Method	_strippedLines	Undocumented
Method	_call_setup	Calls my `setup` method (almost always your override of that method, actually) and processes any return value.

@classmethod
def correct(cls, Ns):

Returns an approximate correction factor to account for high capacitance readings due to imperfect sampling of the AC test signal.

Call with the number of Ngspice time steps per AC test signal cycle.

@classmethod
def _xl(cls, f, kw):

Called by mc_addedBias and mc_separateBias to make voltage source cmv_xl.

@classmethod
def mc_addedBias(cls, f, npos, nneg, bias, cap, **kw):

Makes an instance of me with bias added to the AC test signal and sent through the matching filter, and connects it to the specified nodes.

Supply the circuit generation tool f as the first argument, followed by the nodes npos, nneg, bias (output, filtered) and cap (output).

Makes a voltage source cmv_xl external to the subcircuit, with DC voltages based on the keyword Ls. AV compatible.

Only call this once per circuit.

Parameters invert_bias Set True to invert voltage applied as bias, for P-channel MOSFETs. The bias output remains positive. (type: bool)

@classmethod
def mc_separateBias(cls, f, npos, nneg, bias_out, cap, bias_m, bias, **kw):

Makes an instance of me with a separate bias output (also sent through the matching filter) and connects it to the specified nodes.

Supply the circuit generation tool f as the first argument, followed by the nodes npos, nneg, bias_out (output, non-filtered), bias_m (measurement point, filter input), bias (output, filtered), and cap (output).

Makes a voltage source cmv_xl external to the subcircuit, with DC voltages based on the keyword Ls. AV compatible.

Only call this once per circuit.

Parameters invert_bias Set True to invert voltage of bias_out, for P-channel MOSFETs. The bias output remains positive. (type: bool)

def sources(self, f):

Undocumented

def lpf(self, f, nin, nout):

Makes a lowpass filter following the cosine product and for the matched copy between filt_in and filt_out.

The filter is Chebychev II. Its frequency response is monotonic in the passband and equiripple in the stopband, which begins at half the frequency of the AC test signal.

def v_x(self, f, wa):

Makes a voltage source v_x with the calculated reactance (90-degree current flow vs voltage), based on current through zero-voltage source Vsh.

If the bias is separate, its current is subtracted from what goes through Vsh, improving accuracy.

Internal nodes:

v_sc: Behavioral voltage soruce for the current multiplied by (mixed with) a 90-degree phase-shifted version (cosine) of the AC test signal.
v_scf: Lowpass filtered version of v_sc, substantially rejecting frequency components fa (non-subtracted DC bias current after mixing) and 2*fa (the sum component of AC current with cosine "local oscillator").

Called by, and only by, v_capacitance.

def v_capacitance(self, f):

Makes a voltage source cap with calculated capacitance, based on squared impedance indicated at node z2 and known series resistance and inductance.

def setup(self, f):

overrides pingspice.circuit.netlist.Subcircuit.setup

Subcircuit definition.

Why use f? Because it's short and a conveniently typed letter on the keyboard.

Override this if your subclass does not reference a param.ParameterFinder subclass via the Finder class attribute. As with Include.setup, your override method can return a dict of attribute names and values to set in my instance.

API Documentation for pingspice, generated by pydoctor at 2021-09-18 08:41:11.

pingspice.lib.active.Capacitance_Meter(Subcircuit) class documentation

`pingspice.lib.active.Capacitance_Meter(Subcircuit)` class documentation