A modulator includes a first converter, a second converter and a mixer. The first converter is configured to receive a first bit and provide a first current that is a function of the first bit. The second converter is configured to receive a second bit and provide a second current that is a function of the second bit. The mixer is configured to receive an input current that is a sum of the first current and the second current and a frequency signal and provide an output signal that is a function of the input current and the frequency signal.
1. A modulator comprising:
a first converter configured to receive a first bit and provide a first current that is a function of the first bit, the first converter including a filter to filter the first bit;
a second converter configured to receive a second bit and provide a second current that is a function of the second bit; and
a mixer that is configured to receive an input current that is a sum of the first current and the second current and a frequency signal and provide an output signal that is a function of the input current and the frequency signal.
2. The modulator of claim 1 , wherein the filter is an low-pass filter.
3. The modulator of claim 1 , wherein the first converter comprises a voltage/current converter.
4. The modulator of claim 3 , wherein the voltage/current converter comprises a current scaling unit.
5. The modulator of claim 4 , wherein the current scaling unit comprises a current mirror.
6. The modulator of claim 1 , wherein the mixer is a Gilbert mixer.
7. The modulator of claim 1 , wherein the mixer is a fully-balanced mixer.
8. A radio frequency digital-to-analog converter comprising:
a parallel input configured to receive a digital word having a plurality of bits;
a plurality of voltage/current converters that are each configured to receive one of the plurality of bits and provide one of a plurality of corresponding currents, wherein at least one of the voltage/current converts is configured to filter a received bit;
an adder that sums the plurality of corresponding currents; and
a mixer that modulates a frequency signal as function of the sum of the plurality of corresponding currents.
9. A method for converting a digital word to a frequency signal, comprising:
providing a digital word having at least a first bit and a second bit;
converting the first bit to a corresponding first current, the converting of the first bit including filtering the first bit;
converting the second bit to a corresponding second current; and
summing at least the first current and the second current; and modulating a carrier frequency signal as function of the sum of the first current and the second current.
10. The method of claim 9 , wherein converting the second bit to the corresponding second current comprises filtering the second bit.
11. The method of claim 9 , wherein converting the first bit to the corresponding first current comprises scaling the first current according to a position of the first bit in the digital word, and wherein converting the second bit to the corresponding second current comprises scaling the second current according to a position of the second bit in the digital word.