Mixer-amplifier for an RF receive chain
A mixer-amplifier of an RF signal including at least an amplifier circuit and a mixing circuit controlled at a local oscillator frequency, for amplifying a signal applied on at least one input terminal and converting a first frequency of this signal into a second, lower, frequency, and including a reverse feedback loop switched at the local oscillator frequency.
1. A mixer-amplifier comprising:
a mixer-amplifier circuit, including an amplifier circuit followed by a mixing circuit, configured to amplify an RF signal applied to the amplifier circuit and to convert a frequency of the RF signal to a lower frequency, the mixing circuit being controlled at a local oscillator frequency; and
a reverse feedback loop including a switch that is switched at the local oscillator frequency, the reverse feedback loop being coupled directly to an output of the mixing circuit and to an input of the amplifier circuit, wherein the mixer-amplifier circuit includes differential inputs and differential outputs and wherein the reverse feedback loop includes a first feedback path comprising a first transistor directly coupled between a + output and a + input and switched by the negative local oscillator signal, a second feedback path comprising a second transistor directly coupled between a − output and the + input and switched by the positive local oscillator signal, a third feedback path comprising a third transistor directly coupled between the + output and a − input and switched by the positive local oscillator signal, and a fourth feedback path comprising a fourth transistor directly coupled between the − output and the − input and switched by the negative local oscillator signal.
2. A mixer-amplifier as defined in claim 1 , wherein the reverse feedback loop further comprises a filter at the local oscillator frequency connected in series with the switch.
3. A mixer-amplifier as defined in claim 1 , wherein the mixer-amplifier circuit has differential inputs and differential outputs.
4. A mixer-amplifier as defined in claim 1 , wherein the mixer-amplifier circuit has a single-ended input and a single-ended output.
5. A mixer-amplifier as defined in claim 1 , wherein the mixing circuit includes a first mixer path between a + input and a + output and switched by the positive local oscillator signal, a second mixer path between the + input and a − output and switched by the negative local oscillator signal, a third mixer path between a − input and the − output and switched by the positive local oscillator signal and a fourth mixer path between the − input and the + output and switched by the negative local oscillator signal.