DSP Blockset    
Unwrap

Unwrap an input containing radian phase angles.

Library

Signal Operations

Description

The Unwrap block removes phase discontinuities in each column of the M-by-N input matrix, u, by adding or subtracting an appropriate multiple of 2 to each element. The block recognizes a phase discontinuity, or phase jump, whenever a given input element, ui,j, differs from the preceding element in the same column by an absolute amount greater than the absolute value of the specified Tolerance parameter, .

To eliminate the jumps in the input, the block scans down each column and adds 2k to all elements following a jump (including the discontinuous element itself). The value of k is initialized to 0, and is then incremented by 1 for each successive negative jump in the column (; ), and decremented by 1 for each successive positive jump in the column (; ).

The value of k is reset to 0 for each successive sample-based input. For frame-based inputs, the value of k is retained across successive inputs so that unwrapping can proceed continuously across the frame breaks.

The figure below illustrates a single channel being unwrapped with the default Tolerance setting of . The block recognizes a negative jump of 2 when the ascending sequence of radian phase angles rolls around from  to -. Beginning with the - element, the block adds 2 to all subsequent values in the column. If another negative jump is detected in the same column, the block adds 4 to all subsequent values, and so on.

The output has the same dimension and frame status as the input. For convenience, length-M 1-D vector inputs and sample-based length-M row vector inputs are both treated as M-by-1 column vectors, and the output retains the dimensions of the input.

Dialog Box

Tolerance
The jump size that is recognized as a true phase discontinuity. The default is set to  (rather than a smaller value) to avoid altering legitimate signal features. To increase the block's sensitivity, set Tolerance to a value slightly less than . Tunable, except in Simulink's external mode.

See Also

unwrap
MATLAB


 Uniform Encoder Upsample