DAC with data independent common mode dynamics
A current-steered DAC has first and second differential outputs for providing an analog output signal under control of a digital input signal. In operational use of the DAC, the output signal has a differential component, which is representative of the digital input signal, and also has a first common-mode component. The DAC has circuitry operative to add an extra common-mode component to both the first and second differential outputs so as to make a sum of the first common-mode component and the extra common-mode component substantially independent of a state change of the digital input signal.
1. An electronic circuit comprising a DAC with first and second differential outputs for providing an analog output signal under control of a digital input signal to the DAC, wherein:
in operational use of the DAC, the output signal comprises a differential output signal, which is representative of the digital input signal, and also comprises a first common-mode signal;
the DAC comprises circuitry operative to directly add an extra common-mode signal to both the first and second differential outputs so as to make a sum of the first common-mode signal and the extra common-mode signal substantially independent of a state change of the digital input signal.
2. The circuit of claim 1 , wherein:
the DAC is a current-steering DAC;
the DAC comprises a first current source that is switched to either the first or the second differential output under control of the digital input signal
the circuitry comprises:
a second current source that is switched between two contacts, each connected to the first differential output under control of a digital control signal;
a third current source that is switched between two further contacts, each connected to the second differential output under control of the digital control signal;
the digital input signal and the digital control signal are samples on the same time basis;
first and second subsequent samples of the digital control signal have different states if third and fourth subsequent samples of the digital input signal, coinciding in time with the first and second samples, respectively, have the same states;
the first and second subsequent samples of the digital control signal have the same state if the third and fourth subsequent samples of the digital input signal, coinciding in time with the first and second samples, respectively, have different states.
3. The circuit of claim 2 , wherein:
the first current source comprises a fourth current source and a fifth current source; and
the second, third, fourth and fifth current sources have an identical configuration.