Quadrature circuit for a radio frequency transceiver
The present document describes a quadrature circuit for a radio frequency receiver. The quadrature circuit comprises a first sub-circuit configured to generate a first baseband, BB, signal at an intermediate frequency, IF frequency, from a radio frequency, RF, signal using a local oscillator, LO, signal at a first phase. Furthermore, the quadrature circuit comprises a second sub-circuit configured to generate a second BB signal at the IF frequency from the RF signal using the LO signal at a second phase. The first and second sub-circuit each comprise an oscillator which is locked to the IF frequency.
1 . A quadrature circuit for a radio frequency receiver, wherein the quadrature circuit comprises,
a first sub-circuit configured to generate a first baseband, BB, signal at an intermediate frequency, IF frequency, from a radio frequency, RF, signal using a local oscillator, LO, signal at a first phase; and
a second sub-circuit configured to generate a second BB signal at the IF frequency from the RF signal using the LO signal at a second phase; wherein the first and second sub-circuit each comprise an oscillator which is locked to the IF frequency; wherein
the first and/or the second sub-circuit of the quadrature circuit each comprise a first transistor arranged between a supply voltage and a reference voltage and a second transistor arranged between the supply voltage and the reference voltage;
a drain of the first transistor is coupled with the supply voltage and a source of the first transistor is coupled with the reference voltage;
a drain of the second transistor is coupled with the supply voltage and a source of the second transistor is coupled with the reference voltage;
a gate of the first transistor is coupled with the drain of the second transistor; and
a gate of the second transistor is coupled with the drain of the first transistor.
2 . The quadrature circuit according to claim 1 , wherein the first and/or second sub-circuit comprise a filter unit configured to attenuate signals at frequencies which are greater and/or smaller than the IF frequency.
3 . The quadrature circuit according to claim 2 , wherein the filter unit comprises one or more RC networks.
4 . The quadrature circuit according to claim 2 , wherein the filter unit exhibits a tunable cut-off frequency, in particular using a tunable capacitor.
5 . The quadrature circuit according to claim 1 , wherein the oscillator of the first and/or second sub-circuit comprises a cross-coupled transistor pair.
6 . The quadrature circuit according to claim 5 , wherein the filter unit is arranged as a load of the cross-coupled transistor pair, and wherein the first and/or second sub-circuit comprise a filter unit configured to attenuate signals at frequencies which are greater and/or smaller than the IF frequency.
7 . The quadrature circuit according to claim 1 , wherein
the first sub-circuit comprises a first mixer configured to mix the RF signal with the LO signal at the first phase, to generate a first IF signal; wherein the oscillator of the first sub-circuit is configured to filter and/or to amplify the first IF signal to generate the first BB signal; and
the second sub-circuit comprises a second mixer configured to mix the RF signal with the LO signal at the second phase, to generate a second IF signal; wherein the oscillator of the second sub-circuit is configured to filter and/or to amplify the second IF signal to generate the second BB signal.
8 . The quadrature circuit according to claim 7 , wherein the quadrature circuit comprises a cross-coupling circuit configured to
couple the first IF signal with the second BB signal; and/or
couple the second IF signal with the first BB signal.
9 . The quadrature circuit according to claim 8 , wherein the cross-coupling circuit comprises
a polarity switch configured to switch a polarity of the first IF signal prior to coupling the first IF signal with the second BB signal; and/or
a polarity switch configured to switch a polarity of the second IF signal prior to coupling the second IF signal with the first BB signal.
10 . The quadrature circuit according to claim 1 , wherein the quadrature circuit comprises an adaptive gain control unit configured to adapt a gain of the first and/or second sub-circuit in dependence of a signal level of the first and/or second BB signals.
11 . The quadrature circuit according to claim 1 , wherein
the oscillator of the first and/or second sub-circuit of the quadrature circuit comprises the first transistor arranged between the supply voltage and the reference voltage, and the second transistor arranged between the supply voltage and the reference voltage.
12 . The quadrature circuit according to claim 1 , wherein
a first differential IF signal, which is derived from the RF signal, is applied to the source of the first transistor; and
a second differential IF signal, which is derived from the RF signal, is applied to the source of the second transistor.
13 . The quadrature circuit according to claim 12 , wherein the first and/or the second sub-circuit of the quadrature circuit each comprise
a first switching element configured to couple or to decouple the RF signal to or from the drain of the first transistor in dependence of the LO signal at the first phase or at the second phase, in order to provide the first differential IF signal at the source of the first transistor; and
a second switching element configured to couple or to decouple the RF signal to or from the drain of the second transistor in dependence of the LO signal at the first phase or at the second phase, phase shifted by 90°, in order to provide the second differential IF signal at the source of the second transistor.
14 . The quadrature circuit according to claim 13 , wherein
the first and/or the second sub-circuit of the quadrature circuit each comprise a first variable resistance arranged between the first switching element and the drain of the first transistor;
the first and/or the second sub-circuit of the quadrature circuit each comprise a second variable resistance arranged between the second switching element and the drain of the second transistor; and
the quadrature circuit comprises an adaptive gain control unit configured to adapt the first variable resistance and/or the second variable resistance in dependence of a signal level of the first and/or second BB signals.
15 . The quadrature circuit according to claim 1 , wherein
a first differential BB signal is provided at the drain of the first transistor; and
a second differential BB signal is provided at the drain of the second transistor.
16 . The quadrature circuit according to claim 15 , wherein the quadrature circuit comprises a cross-coupling circuit configured to
couple the source of the first transistor of the first sub-circuit with the drain of the first transistor or with the drain of the second transistor of the second sub-circuit via a switching element controlled in dependence of the first differential BB signal of the first sub-circuit;
couple the source of the second transistor of the first sub-circuit with the drain of the second transistor or with the drain of the first transistor of the second sub-circuit via a switching element controlled in dependence of the second differential BB signal of the first sub-circuit;
couple the source of the first transistor of the second sub-circuit with the drain of the first transistor or with the drain of the second transistor of the first sub-circuit via a switching element controlled in dependence of the first differential BB signal of the second sub-circuit; and
couple the source of the second transistor of the second sub-circuit with the drain of the second transistor or with the drain of the first transistor of the first sub-circuit via a switching element controlled in dependence of the second differential BB signal of the second sub-circuit.
17 . The quadrature circuit according to claim 1 , wherein the first and/or the second sub-circuit of the quadrature circuit each comprise
a first RC circuit arranged between the drain of the first transistor and the supply voltage; and
a second RC circuit arranged between the drain of the second transistor and the supply voltage.
18 . The quadrature circuit according to claim 1 , wherein the first and/or the second sub-circuit of the quadrature circuit each comprise
a first current source arranged between the source of the first transistor and the reference voltage; and
a second current source arranged between the source of the second transistor and the reference voltage.
19 . The quadrature circuit according to claim 1 , wherein the quadrature circuit comprises,
a first analog-to-digital converter configured to convert the first BB signal into a first digital BB signal; and
a second analog-to-digital converter configured to convert the second BB signal into a second digital BB signal.
20 . A method for processing a radio frequency signal; wherein the method comprises,
generating a first baseband, BB, signal at an intermediate frequency, IF frequency, from a radio frequency, RF, signal using a local oscillator, LO, signal at a first phase and using a first oscillator which is locked to the IF frequency; and
generating a second BB signal at the IF frequency from the RF signal using the LO signal at a second phase and using a second oscillator which is locked to the IF frequency; wherein
the first and/or the second oscillator each comprise a first transistor arranged between a supply voltage and a reference voltage, and a second transistor arranged between the supply voltage and the reference voltage;
a drain of the first transistor is coupled with the supply voltage and a source of the first transistor is coupled with the reference voltage;
a drain of the second transistor is coupled with the supply voltage and a source of the second transistor is coupled with the reference voltage;
a gate of the first transistor is coupled with the drain of the second transistor; and
a gate of the second transistor is coupled with the drain of the first transistor.