Radio frequency transceiver sytem, local oscillator unit and method

Abstract

A Radio Frequency, RF, transceiver system is provided. The system comprises a frequency mixer configured to receive a first bias voltage and a local oscillator, LO, bias. The first bias voltage is a Direct Current, DC, voltage and the LO bias is an Alternating Current, AC, voltage. The system further comprises an LO distribution network configured to generate the LO bias voltage. The system further comprises a transimpedance amplifier configured to receive a second bias voltage. The second bias voltage is a DC voltage. The RF transceiver system is configured to operate in first mode or a second mode. The first mode comprises a normal mode and the second mode comprises a detector mode. The detector mode enables a determination of an amplitude of the LO bias voltage.

Description

[0001] RADIO FREQUENCY TRANSCEIVER SYTEM, LOCAL OSCILLATOR UNIT AND METHOD

[0002] TECHNICAL FIELD

[0003] Embodiments herein relate to a radio frequency transceiver system, a local oscillator unit and methods therein. In some aspects, they relate to determining an amplitude of a local oscillator signal.

[0004] BACKGROUND

[0005] A typical radio frequency (RF) circuit with some medium- to high- integration contains frequency up- and down-conversion via mixers. The down converting mixer has an RF input and a known unmodulated frequency, to produce a down converted signal. The up-conversion mixer works in the opposite direction to generate a modulated RF frequency from a modulated low frequency signal. In both cases, the known unmodulated frequency is needed, it is often referred to as local oscillator (LO) signal, as it is generated from a local, to the system, oscillator, that is well controlled in terms of frequency, amplitude, and noise. The LO signal is however one of the very highest frequencies of the system, and typically the LO distribution network and mixer input needs to be meticulously designed to have the wanted signal characteristics at the mixer element. In an actual system, control of and knowledge of LO quality at mixer becomes a real problem.

[0006] One solution is to try to discern the quality of the LO by looking at signal chain inputoutput relations. One could adjust parameters of the LO path, and settle for the situation with the best performance, such as highest signal gain, lowest signal noise etc.

[0007] Another solution to the LO adjustment issue that is sometimes used is to design a dedicated “peak-detector” that measures the amplitude of the LO signal at suitable points in the circuit.

[0008] SUMMARY

[0009] As a part of developing embodiments herein a problem was identified by the inventors and will first be discussed.

[0010] It is very hard to know the LO quality from only looking at signal input / output characteristics. So many other factors contribute. For instance, at a room temperature thecharacteristics can be satisfactory for a wide range of LO settings, with very little difference, because the LO signal chain works in a clipped behavior. But when operating at temperature extremes, the signal properties suddenly become much more sensitive to LO settings, as the LO signal is at some limit of operation.

[0011] It is also so that in an a down conversion, such as receiver, application, one does not have control of the signal input, the antenna. There is no controllable signal source. In this case the input-output method cannot be used.

[0012] The solution with dedicated peak detector circuit adds area, power, and especially it will load the signal capacitively. The loading causes the LO signal strength to be reduced from the measurement. The higher the frequency, the more sensitive the path is. For millimeter wave communications, it is often unfeasible with dedicated detectors.

[0013] An object of embodiments herein is to improve LO signal sensing in an RF circuitry.

[0014] According to an aspect of embodiments herein, the object is achieved by a Radio Frequency, RF, transceiver system.

[0015] The system comprises a frequency mixer configured to receive a first bias voltage and a local oscillator, LO, bias voltage. The first bias voltage is a Direct Current, DC, voltage and the LO bias voltage is an Alternating Current, AC, voltage. The system further comprises an LO distribution network configured to generate the LO bias voltage, the system further a transimpedance amplifier configured to receive a second bias voltage. The second bias voltage is a DC voltage.

[0016] The RF transceiver system is configured to operate in first mode or a second mode. The first mode comprises a normal mode and the second mode comprises a detector mode. The detector mode enables a determination of an amplitude of the LO bias voltage.

[0017] According to an aspect of embodiments herein, the object is achieved by a method for determining an amplitude of Local Oscillator, LO, bias in a Radio Frequency, RF, transceiver system. The RF transceiver system comprises a frequency mixer, an LO distribution network and a transimpedance amplifier.

[0018] The RF transceiver system is operated in a first mode. The first mode is normal mode.

[0019] A second mode is activated. The second mode triggers the RF transceiver system to operate in the second mode. The second mode comprises a detector mode.

[0020] The amplitude of the LO bias voltage is determined.According to an aspect of embodiments herein, the object is achieved by a Local Oscillator, LO, unit configured to determine an amplitude of an LO bias voltage in a Radio Frequency, RF, transceiver system. The RF transceiver system comprises a frequency mixer, an LO distribution network and a transimpedance amplifier.

[0021] The Lo unit is configured to operate the RF transceiver system in a first mode. The first mode is normal mode.

[0022] The LO unit is configured to activate a second mode. The second mode triggers the RF transceiver system to operate in the second mode. The second mode comprises a detector mode.

[0023] The LO unit is configured to determine the amplitude of the LO bias voltage.

[0024] BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Examples of embodiments herein are described in more detail with reference to attached drawings in which:

[0026] Figure 1 illustrates an example according to embodiments herein.

[0027] Figure 2 is a flowchart depicting embodiments of a method.

[0028] Figure 3a illustrates an example according to embodiments herein.

[0029] Figure 3b illustrates an example according to embodiments herein.

[0030] Figure 4 illustrates an example according to embodiments herein.

[0031] Figure 5 illustrates an example according to embodiments herein.

[0032] Figure 6 illustrates an example according to embodiments herein.

[0033] Figure 7 illustrates an example according to embodiments herein.

[0034] Figure 8 is a schematic block diagram illustrating embodiments of an LO unit.

[0035] DETAILED DESCRIPTION

[0036] Embodiments herein relate to LO signal sensing in an RF circuitry.

[0037] Examples of embodiment herein allow sensing the LO amplitude by reconfiguring the mixer circuitry to function in an alternate mode, as a detector circuit. The reconfiguring may e.g., be done solely by changing low frequency nodes, meaning that no high frequency signal paths are degraded by adding the sensing mode to the circuitry.According to examples of embodiments herein, the signal quality of the LO signal is sensed unobtrusively. The sensing may e.g., permit an optimization that is independent of the signal path characteristics and independent of any high frequency measurement equipment.

[0038] Examples of embodiments herein may e.g., provide the advantages that no loading of the LO signal in normal usage by extra circuitry is performed. Further, examples of embodiments herein may provide the advantage of sensing the LO quality without access to circuit input and output, for in application tuning. Yet further, examples of embodiments herein may e.g., provide an area and power efficient mechanism for sensing the LO signal. Yet further, examples of embodiments herein may provide design for test advantage, as it gives the possibility to test a high frequency requirement without any dedicated high frequency test instruments.

[0039] According to examples of embodiments herein, an RF transceiver system 100 is provided. An example of the RF transceiver system 100 shown in Figure 1.

[0040] The RF transceiver system 100 comprises a frequency mixer 110. The frequency mixer 110 may be configured to perform upconversion and / or downconversion of signal. The frequency mixer 110 may be configured to receive a first bias voltage (101) and a LO bias voltage (121). The first bias voltage may e.g., comprise a first Direct Current (DC) voltage. The LO bias voltage may e.g., comprise an Alternating Current (AC) voltage.

[0041] The RF transceiver system 100 further comprises an LO distribution network 120.

[0042] The LO distribution network 120 may be configured to distribute an LO signal, such as the LO bias voltage 121, from a Phase Lock Loop (PLL) to the frequency mixer 110.

[0043] The RF transceiver system 100 further comprises a transimpedance amplifier 130. The transimpedance amplifier 130 may e.g., be configured to convert a current to a voltage. The transimpedance amplifier 130 may e.g., be configured to receive a second bias voltage. The second bias voltage may comprise a second DC bias voltage 131.

[0044] According to examples of embodiment herein, the RF transceiver system 100 is configured to operate in a first mode or a second mode. The first mode comprises a normal mode, e.g., where the frequency mixer 110 performs upconversion or downconversion of signals. The second mode comprises a detector mode. In the detector mode, the amplitude of the LO bias may be determined.According to some examples, the detector mode may be activated be increasing the first bias voltage. This results in the first bias voltage is higher than the second bias voltage. In the normal mode the first bias voltage and the second bias voltage are equal, i.e. , they have the same voltage level.

[0045] By increasing the first bias voltage, and thus activating the detector mode, a current will flow through the frequency mixer 110. The current comprises a DC current. The DC current will flow through the frequency mixer 110 and through one or more feedback buffer resistor in the transimpedance amplifier 130. The level of the DC current may be dependent on the LO bias voltage. Thus, there is a correlation, in the detector mode, between the DC current and the LO bias voltage that may be utilized to determine the amplitude of the LO bias voltage.

[0046] The determination of the amplitude of the LO bias voltage may be based on a DC voltage of the DC current. Thus, the DC voltage may need to be determined. The DC voltage may be based on the DC current and a feedback resistor value, such as a resistor value of the one or more buffer feedback resistors. The DC voltage may thus equal the DC current multiplied with the feedback resistor value.

[0047] According to examples of embodiments herein, the amplitude of the LO bias is determined based on the DC voltage, e.g., measured, at an input of the transimpedance amplifier 130. In other examples, the DC voltage is the DC voltage at, e.g., measured at, a bias node of an operational amplifier in the transimpedance amplifier 130. The latter may comprise that the transimpedance amplifier comprises a probe measuring the DC voltage at the bias node of the operational amplifier. This may be reduce the risk of degradation of the normal mode operation.

[0048] According to some examples of embodiments herein, the RF transceiver system 100 comprises a replica circuitry 140. The replica circuitry 140 may e.g., be a replica of the frequency mixer 110 and the transimpedance amplifier 130. This may e.g., mean that the replica circuitry 140 comprises a frequency mixer 141 that is identical to the frequency mixer 120, and a transceiver amplifier 142 that is identical to the transimpedance amplifier 130. The replica circuitry 140 is fed the same bias voltages as is fed to the frequency mixer 120 and the transimpedance amplifier 130. This may mean that the frequency mixer 141 receives the first bias voltage and the transimpedance amplifier 142 receives the second bias voltage. From the replica circuitry 140, a reference DC voltage may be determined. The DC reference voltage may be determined in the same way as described above for DC voltage.The DC reference voltage may be used to determine the amplitude of the LO bias voltage. E.g., the amplitude of the LO bias voltage may be determined as a function of the difference between the reference DC voltage and the DC voltage. By using the replica circuitry 140 and the reference DC voltage, the signal dependent part of the DC voltage, such as the part of the DC voltage dependent of the LO bias voltage, may be isolated from background level. This increases the accuracy of the amplitude determination since all DC levels in the RF transceiver system 100 may vary with process voltage and temperature.

[0049] Figure 2 shows example embodiments of a method for determining the amplitude of the LO bias voltage in the RF transceiver system 100. The RF transceiver system 100 comprises the frequency mixer 110, the LO distribution network 120 and the transimpedance amplifier 130. The LO distribution network 120 generate AC LO bias voltage. The frequency mixer 110 may e.g., receive the first DC bias voltage and the AC LO bias voltage. The transimpedance amplifier 130 may e.g., receive the second DC bias voltage. The method comprises the following actions, which actions may be taken in any suitable order. Actions that are optional are presented in dashed boxes in Figure 2.

[0050] Action 201

[0051] The RF transceiver system 100 is operated in the first mode. The first mode is such as comprises, a normal mode. The normal mode may e.g., mean that the frequency mixer 110 performs upconversion or downconversion of signals.

[0052] Action 202

[0053] A second mode is activated. The second mode triggers the RF transceiver system 100 operate in the second mode. The second mode comprises a detector mode. In the detector mode, the amplitude of the LO bias voltage may be determined.

[0054] Action 203

[0055] The amplitude of the LO bias voltage is determined.

[0056] In some embodiments, activating the detector mode comprises increasing the first DC bias voltage. This may e.g., mean that the after increasing the first bias voltage, the first bias voltage is higher than the second bias voltage. This since, in some embodiments, in the normal mode the first DC bias voltage and second DC bias voltage are equal. The result of increasing the first bias voltage may e.g., mean that a voltage drop is introduced over the frequency mixer 110.Therefore, in some embodiments, when operating in the detector mode, and after the first bias voltage has been increased, a DC current will flow through the frequency mixer 110 and through one or more feedback buffer resistor in the transimpedance amplifier 130. The DC current is dependent on the LO bias amplitude. Thus, there is a correlation, in the detector mode, between the DC current and the LO bias voltage that may be utilized to determine the amplitude of the LO bias voltage.

[0057] In some embodiments, the DC voltage is based on the DC current and a feedback resistor value. Thus, the DC voltage may need to be determined. The DC voltage may be based on the DC current and a feedback resistor value, such as a resistor value of the one or more buffer feedback resistors. The DC voltage may thus equal the DC current multiplied with the feedback resistor value.

[0058] In some embodiments, the LO bias amplitude is determined based on a DC voltage at an input of the transimpedance amplifier 130. In other embodiments, the LO bias amplitude is determined based on a DC voltage at a bias node of an operational amplifier comprised in the transimpedance amplifier 130.

[0059] In some embodiments, the RF transceiver system 100, as mentioned above, comprises the replica circuit 140. The replica circuit 140 is a replica of the frequency mixer 110 and the transimpedance amplifier 130 with the same first DC bias voltage and second DC bias voltage. This may e.g., mean that the replica circuitry 140 comprises a frequency mixer 141 that is identical to the frequency mixer 120, and a transceiver amplifier 142 that is identical to the transimpedance amplifier 130. The replica circuitry 140 is fed the same bias voltages as is fed to the frequency mixer 120 and the transimpedance amplifier 130. This may mean that the frequency mixer 141 receives the first bias voltage and the transimpedance amplifier 142 receives the second bias voltage.

[0060] In some embodiments the reference DC voltage is determined from the replica circuitry 140. The reference DC voltage may be determined the same way as described above.

[0061] In some embodiments, the LO bias amplitude is determined as function of the difference between the reference DC voltage and DC voltage. E.g., the amplitude of the LO bias voltage may be determined as a function of the difference between the reference DC voltage and the DC voltage. By using the replica circuitry 140 and the reference DC voltage, the signal dependent part of the DC voltage, such as the part of the DC voltage dependent of the LO bias voltage, may be isolated from background level. This increases the accuracy of the amplitude determination since all DC levels in the RF transceiver system 100 may vary with process voltage and temperature.Embodiments herein such as the embodiments mentioned above will now be further described and exemplified. The text below is applicable to embodiments herein and may be combined with any suitable embodiment described above.

[0062] In its simplest, as shown in Figure 3a, form the system is a frequency mixer with an input and an output, where the system needs a good signal on the LO signal, and one needs some observation capability. In this example a down conversion mixer is described.

[0063] In a real-world case, the LO signal may come from an integrated Phase locked loop (PLL) that has many settings influencing the LO amplitude. Then there is a LO distribution path that can involve several stages, possibly amplifiers with tunable resonator tanks and may also contain dividers or multiplier blocks. With all these signals, the output of the PLL is not the desired knowledge. The desired knowledge is the actual signal quality at the mixer. Figure 3b shows an example of a system with a PLL and an LO distribution network, to highlight where the observation is needed.

[0064] Figure 4 and Figure 5 show an example of how the LO detector may be implemented in a millimeter wave receiver chain with a passive mixer topology. The normal operation is shown in Figure 4 where no voltage is applied across the mixer circuitry. In this case the Direct Current (DC) levels at input and output of the mixer are unaffected by the LO amplitude. In this mode the value of input bias and output bias is chosen to have a good operating point for the transimpedance amplifier on the output. The Io bias, which is the common mode voltage of the differential LO signal, is chosen to be approximately one threshold (Vth) above the input and output bias. This way the duty cycle of the mixer is approximately 50%. However, the exact bias levels affect several RF performance parameters such as noise figure, 2nd order intermodulation (IM2) and gain. So, this may need to be tunable.

[0065] The detector mode is shown in Figure 5 where the DC voltage of the input of the mixer is changed, and now the current flow from RF input (left) to baseband output (right) is dependent on the signal amplitude of the LO. The LO signal is at high frequency, but the mixer transistors act as a rectifier circuit, and will therefore create a DC component, i_dc, that can be statically measured.

[0066] The change in DC current due to a LO signal presence can be detected in several ways. The target is that the detection should not interfere with the normal mode.In the case shown, with a transimpedance amplifier at the mixer output, the DC current will create a corresponding de voltage at the transimpedance amplifier input, where the voltage is set by the current, times the feedback resistor value. The detector output will therefore be possible to measure as a Voltage = (rfeedb x i_dc).

[0067] As an extra precaution, one may avoid adding any sensing at the transimpedance amplifier input and place the probe inside the transimpedance amplifier. An example is shown in Figure 6, where the voltage is sensed at the operational amplifier bias node, which results in a constant DC shift down from the transimpedance amplifier input.

[0068] Figure 5. Example of isolating the transimpedance amplifier sensing port.

[0069] The measurement up to this point will result in a de test output that is monotonically increasing with LO amplitude on the mixer. However, all the de levels in the circuit, will vary with process voltage and temperature, such that it will not be possible to make any conclusion absolute levels. However, by adding an extra replica branch, with similar devices and bias levels, it will be possible to isolate the signal dependent part from the de level background. Such a replica circuitry is shown in Figure 6. Notice that the replica design is using the same reference voltages as the actual mixer. This means that any change in bias levels chosen for the normal operation will have a similar effect on the replica branch, and the detector measurement is not degraded.

[0070] The most important feature of the detector is the monotonicity and deterministic operation. A known detector gain is some extra benefit, as it can be used for production test sorting of known good die without using any RF production equipment, and it can be used for optimizing power dissipation in application.

[0071] Figure 6. Example of replica circuitry to create a reference voltage independent of the LO detector. The devices inside the dashed rectangle are needed in case the isolation circuitry of previous figure is used. Otherwise, this part can be a direct connection.

[0072] The test of how the LO detector circuit works over environmental and process variation is simulated in a MMW circuit design. The design was analyzed over process temperature and frequency.

[0073] As the design is essentially a square law amplitude detector, the results are analyzed as a log-log behavior, where the input is the amplitude of the differential signal on the mixer transistors, and the output is the DC voltage response of the detector, wherethe measured test output is the difference of the detector voltage to the reference voltage of the replica circuit.

[0074] The scatter data is then used to estimate how well one can predict the detector response, and use it to deduce the LO amplitude from detector readout. From this data an error within + / - 2dB is estimated.

[0075] According to some examples of embodiments herein, an LO unit 105 is configured perform the method actions above. The LO unit 105 is configured to determine an amplitude of an LO bias in the RF transceiver system 100. The LO unit 105 may be comprised in the RF transceiver system 100. Alternatively, the LO unit 105 may be connected to the RF transceiver system 100. The LO unit 105 may comprise an arrangement depicted in Figure 8.

[0076] The LO unit 105 may comprise an input and output interface 30 configured to communicate with each other. The input and output interface 30 may comprise a receiver, e.g. wired and / or wireless, (not shown) and a transmitter, e.g. wired and / or wireless, (not shown).

[0077] The embodiments herein may be implemented through a respective processor or one or more processors, such as at least one processor 31 of a processing circuitry in the LO unit 105 in Figure 8, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code for performing the embodiments herein when being loaded into the LO unit 105. One such carrier may be in the form of a CD ROM disc. It is however feasible with other data carriers such as a memory stick. The computer program code may furthermore be provided as pure program code on a server and downloaded to the LO unit 105.

[0078] The LO unit 105 and / or processor 30 is configured to determine an amplitude of an LO bias in the RF transceiver system 100. The RF transceiver system 100 is configured to comprising the frequency mixer 110, the LO distribution network 120 and the transimpedance amplifier 130:

[0079] The LO unit 105 and / or processor 30 is configured to operate the RF transceiver system 100 in a first mode. The first mode is normal mode.The LO unit 105 and / or processor 30 is configured to activate a second mode. Activating the second mode triggers the RF transceiver system 100 operate in the second mode. The second mode comprises a detector mode.

[0080] The LO unit 105 and / or processor 30 is configured to determine the amplitude of the LO bias.

[0081] In some embodiments, the LO distribution network 120 is generating an Alternating Current, AC, LO bias voltage.

[0082] In some embodiments, the frequency mixer 110 is receiving a first Direct Current, DC, bias voltage and the AC LO bias voltage.

[0083] In some embodiments, the transimpedance amplifier 130 is receiving a second DC bias voltage.

[0084] In some embodiments, activating the detector mode comprises increasing the first DC bias voltage.

[0085] In some embodiments, in the normal mode the first DC bias voltage and second DC bias voltage are equal.

[0086] In some embodiments, when operating in the detector mode, a DC current will flow through the frequency mixer 110 and through one or more feedback buffer resistor in the transimpedance amplifier 130. The DC current is dependent on the LO bias 121 amplitude.

[0087] In some embodiments, the LO bias 121 amplitude is determined based on a DC voltage 132 at an input of the transimpedance amplifier 130. The DC voltage is based on the DC current and a feedback resistor value.

[0088] In some embodiments, the LO bias 121 amplitude is determined based on a DC voltage 132 at a bias node of an operational amplifier 133 comprised in the transimpedance amplifier 130. The DC voltage is based on the DC current and a feedback resistor value.

[0089] In some embodiments, the RF transceiver system 100 comprises a replica circuit 140. The replica circuit 140 being a replica of the frequency mixer 110 and the transimpedance amplifier 130 with the same first DC bias voltage 101 and second DC bias voltage 131. Determining the amplitude of the LO bias voltage comprises determining a reference DC voltage from the replica circuitry 140.

[0090] In some embodiments, the LO bias amplitude is determined as function of the difference between the reference DC voltage and DC voltage.The LO unit 105 may further comprise respective a memory 32 comprising one or more memory units. The memory 32 comprises instructions executable by the processor 31 in the LO unit 105.

[0091] The memory 32 is arranged to be used to store instructions, data, configurations, handovertiming conditions, handovertiming condition data, requests, responses, messages, identifiers, indications, parameters, applications to perform the methods herein when being executed in the LO unit 105.

[0092] In some embodiments, a computer program 33 comprises instructions, which when executed by the at least one processor 31, cause the at least one processor 31 of the LO unit 105 to perform the actions above.

[0093] In some embodiments, a respective carrier 34 comprises the respective computer program 33, wherein the carrier 34 is one of an electronic signal, an optical signal, an electromagnetic signal, a magnetic signal, an electric signal, a radio signal, a microwave signal, or a computer-readable storage medium.

[0094] Thus, embodiments herein may disclose the LO unit 105 is configured to determine an amplitude of an LO bias in the RF transceiver system 100. The LO unit 105 comprises the processor 31 and the memory 32, said memory 32 comprising instructions executable by said processor 31 whereby said LO unit 105 is operative to perform any of the methods herein.

[0095] As will be readily understood by those familiar with communications design, that functions means or modules may be implemented using digital logic and / or one or more microcontrollers, microprocessors, or other digital hardware. In some embodiments, several or all of the various functions may be implemented together, such as in a single application-specific integrated circuit (ASIC), or in two or more separate devices with appropriate hardware and / or software interfaces between them. Several of the functions may be implemented on a processor shared with other functional components of a base station, for example.

[0096] Alternatively, several of the functional elements of the processing means discussed may be provided through the use of dedicated hardware, while others are provided with hardware for executing software, in association with the appropriate software or firmware. Thus, the term “processor” or “controller” as used herein does not exclusively refer to hardware capable of executing software and may implicitly include, without limitation, digital signal processor (DSP) hardware, read-only memory (ROM) for storing software, random-access memory for storing software and / or program or application data, and nonvolatile memory. Other hardware, conventional and / or custom, may also be included.Designers of communications receivers will appreciate the cost, performance, and maintenance trade-offs inherent in these design choices.

[0097] Any appropriate steps, methods, features, functions, or benefits disclosed herein may be performed through one or more functional units or modules of one or more virtual apparatuses. Each virtual apparatus may comprise a number of these functional units. These functional units may be implemented via processing circuitry, which may include one or more microprocessor or microcontrollers, as well as other digital hardware, which may include digital signal processors (DSPs), special-purpose digital logic, and the like. The processing circuitry may be configured to execute program code stored in memory, which may include one or several types of memory such as read-only memory (ROM), random-access memory (RAM), cache memory, flash memory devices, optical storage devices, etc. Program code stored in memory includes program instructions for executing one or more telecommunications and / or data communications protocols as well as instructions for carrying out one or more of the techniques described herein. In some implementations, the processing circuitry may be used to cause the respective functional unit to perform corresponding functions according one or more embodiments of the present disclosure.

Claims

Claims1. A Radio Frequency, RF, transceiver system (100) comprising:a frequency mixer (110) configured to receive a first bias voltage (101) and a local oscillator, LO, bias (121), wherein the first bias voltage (101) is a Direct Current, DC, voltage and the LO bias is an Alternating Current, AC, voltage,an LO distribution network (120) configured to generate the LO signal (121), a transimpedance amplifier (130) configured to receive a second bias voltage (131), wherein the second bias voltage is a DC voltage,wherein the RF transceiver system is configured to operate in first mode or a second mode, the first mode comprising a normal mode and the second mode comprising a detector mode, wherein the detector mode enables a determination of an amplitude of the LO bias (121).

2. The RF transceiver system according to clam 1 , wherein the detector mode is activated by increasing the first bias voltage (101).

3. The RF transceiver system (100) according to any of claims 1-2, wherein in the normal mode the first bias voltage (101) and second bias voltage are equal.

4. The RF transceiver system (100) according to any of claims 1-3, wherein when operating in the detector mode, a DC current will flow through the frequency mixer (110) and through one or more feedback buffer resistor in the transimpedance amplifier (130), and wherein the DC current is dependent on the LO bias (121) amplitude.

5. The RF transceiver system (100) according to claim 4, wherein the LO bias (121) amplitude is determined based on a DC voltage (132) at an input of the transimpedance amplifier (130), which DC voltage is based on the DC current and a feedback resistor value.

6. The RF transceiver system (100) according to any of claims 4-5, wherein the RF transceiver system (100) comprises a replica circuit (140), the replica circuit being a replica of the frequency mixer (110) and the transimpedance amplifier (130) with the same first bias voltage (101) and second bias voltage (131), and wherein a reference DC voltage is determined from the replica circuitry (140).

7. The RF transceiver system (100) according to claim 6, wherein the LO bias amplitude is determined as function of the difference between the reference DC voltage and DC voltage.

8. A method for determining an amplitude of Local Oscillator, LO, bias in a Radio Frequency, RF, transceiver system (100), the RF transceiver system (100) comprising a frequency mixer (110), an LO distribution network (120) and a transimpedance amplifier (130), the method comprising:operating (201) the RF transceiver system (100) in a first mode, which first mode is normal mode,activating (202) a second mode, triggering the RF transceiver system (100) operate in the second mode, which second mode comprises a detector mode, and determining (203) the amplitude of the LO bias.

9. The method according to claim 8, wherein:- the LO distribution network (120) is generating an Alternating Current, AC, LO bias voltage,- the frequency mixer (110) is receiving a first Direct Current, DC, bias voltage and the AC LO bias voltage,- the transimpedance amplifier (130) is receiving a second DC bias voltage, and wherein activating the detector mode comprises increasing the first DC bias voltage.

10. The method according to claim 9, wherein in the normal mode the first DC bias voltage and second DC bias voltage are equal.

11. The method according to any of claims 8-10, wherein when operating in the detector mode, a DC current will flow through the frequency mixer (110) and through one or more feedback buffer resistor in the transimpedance amplifier (130), and wherein the DC current is dependent on the LO bias (121) amplitude.

12. The method according to claim 11 , wherein the LO bias (121) amplitude is determined based on a DC voltage (132) at an input of the transimpedance amplifier (130), which DC voltage is based on the DC current and a feedback resistor value.

13. The method according to claim 11, wherein the LO bias (121) amplitude is determined based on a DC voltage (132) at a bias node of an operational amplifier (133) comprised in the transimpedance amplifier (130), which DC voltage is based on the DC current and a feedback resistor value.

14. The method according to any of claims 11-13, wherein the RF transceiver system (100) comprises a replica circuit (140), the replica circuit (140) being a replica of the frequency mixer (110) and the transimpedance amplifier (130) with the same first DC bias voltage (101) and second DC bias voltage (131), and wherein determining the amplitude of the LO bias voltage comprises determining a reference DC voltage from the replica circuitry (140).

15. The method according to claim 14, wherein the LO bias amplitude is determined as function of the difference between the reference DC voltage and DC voltage.

16. A Local Oscillator, LO, unit (105) configured to determine an amplitude of an LO bias in a Radio Frequency, RF, transceiver system (100), the RF transceiver system (100) comprising a frequency mixer (110), an LO distribution network (120) and a transimpedance amplifier (130), the LO unit (105) further being configured to:operate the RF transceiver system (100) in a first mode, which first mode is normal mode,activate a second mode, triggering the RF transceiver system (100) operate in the second mode, which second mode comprises a detector mode, anddetermine the amplitude of the LO bias.

17. The LO unit (105) according to claim 16, wherein the LO unit (105) is configure to be comprised in the RF transceiver system, or connected to the RF transceiver system 100, according to any of claims 1-7.

18. The LO unit (105) according to any of claims 16-17, wherein the LO unit (105) is further configured to perform the method according to any of claims 8-15.

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