Influence of Output Impedance Variations
Using the current-steering DAC Sec. 2.2 , it is easily seen that the output impedance of the converter is signal-dependent, since any non-ideal current source has a finite output impedance. Dependent on what code is applied, different numbers of current sources are connected to the output. The whole DAC can briefly be modeled as a current source, shown in Fig. 3-3, where the output is terminated with a load resistance RL. Figure 3-3 Current source, I5X , with finite output resistance, Rs X ....
A CMOS Oversampling DAC for ADSL Applications
In this chapter the design of a 14-bit 3V-5V CMOS OSDAC for ADSL applications is presented. The work is done by J. J. Wikner Linkoping University , Y. Gao ESDLab, KTH , and N. Tan GlobeSpan Semiconductor . The converter is fabricated in Ericsson's 0.6mm CMOS process. As a very important design issue, the simulation of the whole converter on higher level will be discussed. We show the impact of different filter orders interpolation, FIR and analog , and how this applies to the ADSL standard. In...
Error Feedback Modulator
The error feedback modulator uses the quantization error to feed back 37 , as shown in Fig. 2-9. The quantization error, q nT _ y nT - w nT , is given by the LSBs of the input signal to the quantizer, w nT , and the output signal y n is the MSB of w nT . In the frequency domain, the quantization error signal is W z H z X z - G z Q z which gives Y z H z X z 1 - H z G z Q z Figure 2-9 Basic principle of an error feedback modulator. The signal transfer function, STF z , is STF z H z and the noise...
SemiDigital FIR Filter
For multi-bit modulators, the digital output signal is converted into an analog using a DAC with a smaller resolution than the input signal to the whole OSDAC. As was discussed in Part B Nyquist-Rate Digital-to-Analog Converters for VDSL Applications the linearity is dependent on the reference currents in the DAC. For the single-bit modulators, the output consists of only two levels and the DAC converting this signal can be considered to be completely linear since the two conversion levels...
Analog Smoothing Filter
The output of the semi-digital filter still contains images in the frequency domain due to the sample-and-hold elements. With an analog continuous-time lowpass filter CT LP , Fig. 2-12, the images and noise at higher frequencies above the original wanted bandwidth are attenuated. Figure 2-12 Images and noise are attenuated using the continuous-time filter Figure 2-12 Images and noise are attenuated using the continuous-time filter In addition, in front of the continuous-time filter, also an...
Papers and Conference Contributions
In this section papers and publications with Wikner as author co-author are presented. For overall background description of design, simulation, telecommunication standards, etc., we use papers as N. Tan, J. Erlands, and J. J. Wikner, Fully Differential Line Driver, Pending Swedish Patent, 67 . N. Tan and J. J. Wikner, A CMOS Digital-to-Analog Converter Chipset for Telecommunications, IEEE Magazine on Circuits and Devices, vol. 13, no. 5, pp. 11-16, Sept. 1997, 68 . H. Traff and J. J. Wikner,...