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Dynamic Element Matching Method for D/A Converters

IP.com Disclosure Number: IPCOM000022637D
Original Publication Date: 2004-Apr-25
Included in the Prior Art Database: 2004-Apr-25
Document File: 3 page(s) / 172K

Publishing Venue

Siemens

Related People

Juergen Carstens: CONTACT

Abstract

To achieve low nonlinear distortion results for D/A (Digital-to-Analog) conversions, the use of dynamic element matching (DEM) methods is essential. Apart from the element mismatches, the glitch signals introduced by the switches of the converter add an additional noise floor to the quantization noise floor. Therefore, the number of switches necessary to output a given sequence should be as low as possible. This becomes increasingly significant for new process technologies and in high speed D/A converters. So far, to minimize the glitch signal energy, a restricted randomization technique is used. The disadvantage of this method is that the element mismatch noise is not shaped, resulting in a low signal-to-noise ratio (SNR) in the signal bandwidth. Therefore, it is proposed to incorporate into the restricted randomization technique a mechanism to limit the span of time a single switch can be in one state. All the current sources are summed up and mapped to a voltage at the output. As the control mechanism guarantees that no switch remains in one state (on or off) longer than a predetermined time (number of samples), the spectrum of the output signal of a single switch gets more high frequency components. Thus, the element mismatch noise is changed to a colored high pass noise and the SNR in the signal bandwidth is higher.

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Dynamic Element Matching Method for D/A Converters

Idea: Heinz Koeppl, AT-Graz; Dr. Gernot Kubin, AT-Graz; Dr. Gerhard Paoli, AT-Villach

To achieve low nonlinear distortion results for D/A (Digital-to-Analog) conversions, the use of dynamic element matching (DEM) methods is essential. Apart from the element mismatches, the glitch signals introduced by the switches of the converter add an additional noise floor to the quantization noise floor. Therefore, the number of switches necessary to output a given sequence should be as low as possible. This becomes increasingly significant for new process technologies and in high speed D/A converters. So far, to minimize the glitch signal energy, a restricted randomization technique is used. The disadvantage of this method is that the element mismatch noise is not shaped, resulting in a low signal-to-noise ratio (SNR) in the signal bandwidth.

Therefore, it is proposed to incorporate into the restricted randomization technique a mechanism to limit the span of time a single switch can be in one state. All the current sources are summed up and mapped to a voltage at the output. As the control mechanism guarantees that no switch remains in one state (on or off) longer than a predetermined time (number of samples), the spectrum of the output signal of a single switch gets more high frequency components. Thus, the element mismatch noise is changed to a colored high pass noise and the SNR in the signal bandwidth is higher.

This idea is illustrated in Figure 1. Here x[n] denotes the sequence value at the sample time n. The sequence value in a M-bit converter is represented by the number of voltage or current sources that are switched on. There are 2M cells that can be switched on. For example, the value 3 in a 2-bit

converter can be represented by the unweighted binary expression 1101 and all possible permutations thereof. The control mechanism block consists of an accumulator, which counts the number of samples a particular switch remains in one state. The accumulator is reset to zero if the state of the particular cell is changed. This is performed by the 'MULT' block. The 'THRES' block checks if a switch exceeded the permitted number of samples and, if this is the case, outputs a '1' for this switch. All blocks are acting element-wise on the input and the signals of the bold...