pydsm.delsig.simulateDSM

pydsm.delsig.simulateDSM(u, arg2, nlev=2, x0=0, store_xn=False, store_xmax=False, store_y=False, **options)

Computes the output of a general delta-sigma modulator.

Parameters

uarray_like or matrix_like

modulator input. Multiple inputs are allowed. In this case, u is a matrix with as many rows as the desired inputs

arg2tuple

modulator structure in ABDC matrix form or modulator NTF as zpk tuple. In the latter case, the modulator STF is assumed to be unitary.

nlevint or array of ints, optional

number of levels in quantizer. Multiple quantizers can be specified by making nlev a vector. Defaults to 2.

x0array_like of reals or 0

modulator intitial state vector. Assigning it to 0 is a shorthand for an appropriate length zero vector. Defaults to 0.

store_xnbool, optional

switch controlling the storage of state evolution. See description of return values. Defaults to False.

store_xmaxbool, optional

switch controlling the storage of maxima in state variables. See description of return values. Defaults to False.

store_ybool, optional

switch controlling the storage of quantizer input values. See description of return values. Defaults to False.

Returns

vndarray

samples at the output of the modulator, one per input sample. If there are multiple quantizers, then v is a matrix, with as many columns as the number of samples and as many rows as the number of quantizers.

xnndarray

internal state of the modulator. If store_xn is set to True, then it includes a state snapshot per input sample. In this case, xn is a matrix, with as many columns as the number of samples and as many rows as the number of state variables. If store_xn is False, then xn is a vector containing a snapshot of the last state.

xmaxndarray

maximum absolute value reached by the state variables. If store_xmax is set to True, then xmax is a vector with as many entries as the number of state variables. Otherwise it is null.

yndarray

samples at the quantizer input(s), one per input sample. If store_y is set to True, then y records the quantizer(s) input(s). If there are multiple quantizers, then y is a matrix, with as many columns as the number of samples and as many rows as the number of quantizers. If store_y is False, then y is null.

Other Parameters

backendstring

Use: ‘auto’ for automatic selection; ‘scipy’ for pure python simulator; ‘cblas’ for simulator using platform cblas library; ‘scipy_blas’ for simulator using scipy provided blas. Defaults can be set by changing the function default_options attribute.

Raises

ValueError

‘Incorrect modulator specification’, if the modulator specification is inconsistent.

‘Invalid argument: nlev must be convertible into a 1D int array’, if the quantizer specification is incorrect.

‘Invalid argument: u must be convertible into a 2D float array’, if the input specification is incorrect.

‘Incorrect initial condition specification’ if the initial condition specification for the modulator filters is incorrect.

RuntimeError

‘Unsupported simulator backend xxx’ if an unsupported backend is required

Warns

PyDsmSlowPathWarning

‘Running the slow version of simulateDSM’, if the simulator being used is the slow one, coded in pure Python.

Notes

The quantizer is ideal, producing integer outputs centered about zero. Quantizers with an even number of levels are of the mid-rise type and produce outputs which are odd integers. Quantizers with an odd number of levels are of the mid-tread type and produce outputs which are even integers.

The modulator structure being simulated is a block diagonal one, as returned by the zpk2ss function.

Setting store_xn, store_xmax and store_y to False speeds up the operation.

There are actually two simulators, sharing this function as a front end. One of them is coded in pure python and quite slow. The other one is coded in C (actually in Cython), and directly accesses low level cblas functions. The codebase to be used is controlled by the module switch use_fast_simulator.