Balun mixer circuits
View Patent ↗A single-balanced balun mixer circuit includes a balun with a center tap connected to a differential pair with a tail resistor. The balun receives a first input signal and a second signal at the single-ended input terminal and the center tap, respectively. Such a balun mixer may be used as an up-converter mixer by supplying a baseband or intermediate signal at the center tap and a local oscillator (LO) signal at the single-ended input terminal.
1. A mixer circuit for mixing a local oscillator signal and a baseband signal, comprising:
a balun having a single-ended input terminal and a center tap input terminal, the balun providing balanced output signals wherein the local oscillator signal is provided at the single-ended input terminal and the baseband signal is provided at the center tap input terminal; and
a differential pair including a first transistor and a second transistor and a tail resistor coupled to the first and second transistors, wherein the balanced output signals are provided to the control terminals of the first and second transistors.
2. The mixer circuit of claim 1 , wherein the tail resistor comprises a resistor of variable resistance.
3. The mixer of claim 1 , further comprising:
a second balun having a single-ended input terminal coupled to the single-ended terminal of the first balun, and a center tap input terminal, the balun providing balanced output signals, wherein the baseband signal is a differential signal, the differential signal being provided across the center tap input terminal of the first balun and the center tap input terminal of the second balun, and wherein the local oscillator signal is being provided to the single-ended terminal of the second balun;
a second differential pair including a first transistor and a second transistor and a tail resistor coupled to the first and second transistors; and
coupling capacitors provided across balanced output terminals of the first balun and the second balun, wherein the balanced output signals of the second balun are provided to control terminals of the transistors of the second differential pair, thereby the mixer providing a double-balanced balun mixer.
4. The mixer of claim 3 , further comprising a second double-balanced mixer substantially configured in the same manner as the first double-balanced mixer, wherein the single-ended terminals in the first double-balanced balun mixer and the single-ended terminals in the second double-balanced balun mixer receive inphase and quadrature signals of the local oscillator, and wherein the center tap input terminals of the first double-balanced balun mixer and the center tap input terminals of the second double-balanced balun mixer receive, respectively, the inphase and quadrature differential signals of the baseband signal.
5. The mixer of claim 1 , further comprising an inductor and a capacitor forming a LC filter to provide the inphase and quadrature signals of the local oscillator.
6. The mixer of claim 5 , further comprising polyphase filters provided between the balanced output terminals of the baluns and the control terminals of transistors of the corresponding differential pairs.
7. The mixer of claim 6 , wherein the polyphase filters comprise resistors and capacitors.
8. The mixer of claim 7 , wherein the resistors of the polyphase filters comprise resistors of variable resistance.
9. The mixer of claim 7 , wherein the capacitors of the polyphase filters comprise capacitors of variable capacitance.