Leakage calibration for a frequency converter
Techniques are described for calibration of a frequency converter for reducing a leakage-based direct current component at an output of the frequency converter. In an apparatus comprising a frequency converter arranged to perform frequency conversion on an input signal, a variable load arranged to act on at least one of an input and an output of the frequency converter, and a detector arranged to detect a direct current component of an output signal of the frequency converter, a plurality of states of the variable load are sequentially set, a variation between the direct current components for each one of the plurality of states of the variable load is observed, and at least one parameter influencing the direct current component of the output signal of the frequency converter is adjusted such that the observed variation is reduced.
1. An apparatus comprising:
a frequency converter configured to perform frequency conversion on an input signal, the frequency converter comprising a first mixer and a second mixer;
a variable load configured to act on at least an input of the frequency converter;
a detector configured to detect a direct current component of an output signal of each of the first and second mixers; and
a controller configured to:
set a configuration of the frequency converter such that a local oscillator signal of the first mixer is supplied to a local oscillator input of the first mixer, and a predetermined constant signal is supplied to a local oscillator input of the second mixer;
sequentially set a plurality of states of the variable load;
observe a variation between the direct current components detected by the detector for each one of the plurality of states of the variable load for the output signal of the first mixer; and
adjust at least one parameter of the first mixer influencing the direct current component of the output signal of the first mixer based on the observed variation.
2. The apparatus according to claim 1 , wherein:
the direct current component of the output signal of the first mixer results from a mixing product of the local oscillator signal of the first mixer with a leakage signal component of the local oscillator signal of the first mixer, which appears at the input of the frequency converter and interacts with the variable load acting on the input of the frequency converter.
3. The apparatus according to claim 1 , wherein:
the variable load configured to act on the input of the frequency converter comprises one or more of a short circuit switch of the input of the frequency converter, a switchable shunt resistor connected in parallel to the input of the frequency converter, a switchable capacitor connected in parallel to the input of the frequency converter, or a switch between the input of the frequency converter and at least one signal source of the input signal of the frequency converter.
4. The apparatus according to claim 1 , wherein the controller is configured to:
disconnect the input signal from the input of the frequency converter;
execute at least one of setting the configuration of the frequency converter, observing the variation and adjusting the at least one parameter when the input signal is disconnected from the input of the frequency converter; and
reconnect the input signal to the input of the frequency converter.
5. The apparatus according to claim 1 , wherein:
the first and second mixers are configured to operate with different phases,
the output of the frequency converter comprises one output for each mixer, and
the detector is configured to detect the direct current component of an output signal at each output of the frequency converter.
6. The apparatus according to claim 5 , wherein the at least one parameter comprises one or more of:
a static direct current offset of the first mixer with absence of a local oscillator signal,
a static direct current offset of the first mixer with presence of a local oscillator signal, or
an imbalance at the first mixer.
7. The apparatus according to claim 5 , wherein the controller is configured to set a configuration of the frequency converter in terms of a direct current value of a current source at any one of the outputs of the mixers or in terms of a value of at least one tunable part at any one of the outputs of the mixers.
8. The apparatus according to claim 1 , wherein the apparatus is operable for a receiver of direct conversion type or a receiver of a mixer-first architecture.
9. A method for controlling an apparatus comprising a frequency converter configured to perform frequency conversion on an input signal, the frequency converter comprising a first mixer and a second mixer, a variable load configured to act on at least an input of the frequency converter, and a detector configured to detect a direct current component of an output signal of each of the first and second mixers, the method comprising:
setting a configuration of the frequency converter such that a local oscillator signal of the first mixer is supplied to a local oscillator input of the first mixer, and a predetermined constant signal is supplied to a local oscillator input of the second mixer;
sequentially setting a plurality of states of the variable load;
observing a variation between the direct current components detected by the detector for each one of the plurality of states of the variable load for the output signal of the first mixer; and
adjusting at least one parameter of the first mixer influencing the direct current component of the output signal of the first mixer based on the observed variation.
10. The method according to claim 9 , wherein:
the direct current component of the output signal of the first mixer results from a mixing product of the local oscillator signal of the first mixer with a leakage signal component of the local oscillator signal of the first mixer, which appears at the input of the frequency converter and interacts with the variable load acting on the input of the frequency converter.
11. The method according to claim 9 , wherein:
the variable load configured to act on the input of the frequency converter comprises one or more of a short circuit switch of the input of the frequency converter, a switchable shunt resistor connected in parallel to the input of the frequency converter, a switchable capacitor connected in parallel to the input of the frequency converter, or a switch between the input of the frequency converter and at least one signal source of the input signal of the frequency converter.
12. The method according to claim 9 , further comprising:
disconnecting the input signal from the input of the frequency converter;
executing at least one of setting the configuration of the frequency converter, observing the variation and adjusting the at least one parameter when the input signal is disconnected from the input of the frequency converter; and
reconnecting the input signal to the input of the frequency converter.
13. The method according to claim 9 , wherein:
the first and second mixers are arranged to operate with different phases,
the output of the frequency converter comprises one output for each mixer, and
the direct current component of an output signal is detected at each output of the frequency converter.
14. The method according to claim 13 , wherein the at last one parameter comprises one or more of:
a static direct current offset of the first mixer with absence of a local oscillator signal,
a static direct current offset of the first mixer with presence of a local oscillator signal, or
an imbalance at the first mixer.
15. The method according to claim 13 , wherein the configuration of the frequency converter is set in terms of a direct current value of a current source at any one of the outputs of the mixers or in terms of a value of at least one tumble part at any one of the outputs of the mixers.
16. The method according to claim 9 , wherein the apparatus is operable for a receiver of direct conversion type or a receiver of a mixer-first architecture.
17. An apparatus comprising:
a first mixer;
a second mixer;
a variable load configured to act on inputs of the first and second mixers;
circuitry configured to
control a local oscillator signal of the first mixer to be supplied to a local oscillator input of the first mixer;
control a predetermined constant signal to be supplied to a local oscillator input of the second mixer;
sequentially set a plurality of states of the variable load;
observe a variation between direct current components for the output signal of the first mixer for each one of the plurality of states of the variable load; and
adjust at least one parameter of the first mixer influencing the direct current component of the output signal of the first mixer based on the observed variation.
18. The apparatus of claim 17 , wherein
the first mixer is an in-phase mixer, and
the second mixer is a quadrature mixer.
19. The apparatus of claim 17 , wherein
the first mixer is a quadrature mixer, and
the second mixer is an in-phase mixer.
20. The apparatus of claim 17 , wherein
the apparatus is a mobile terminal configured to communicate via a mobile network.