Patent Description:
In signal transceivers, radio frequency (in particular high frequency, and/or mmWave) signals are detected (measured) by detectors such as peak/rms detectors. Thereby, a control can be achieved over the signal power level. For example, in power amplifiers (in a transmitter), the output power needs to be controlled to meet emission standards, to ensure reliable operation of the devices (for example, transistors) during their operational lifetime, and to reduce power consumption. In order to achieve these needs, capacitive coupling (or attenuation) is typically used to couple the transmitted signals, that should be measured (for example to a signal detector).

Capacitive coupling is generally applied, for example, to reduce the signals to be detected to levels at which the detectors can operate the best, to bias the detector, etc. However, the capacitive couplers/attenuators may introduce uncertainties in the detected signal levels, for example due to variation in the capacitance ratios (e.g. a ratio between a capacitive coupling and a capacitive detector). A reason for these uncertainties may be found in the process variations of the integrated circuit technology process in which the detector circuitry is implemented.

Further, the types of the capacitance used for coupling the signal and for actually detecting the signal are normally different. Conventionally, capacitive ratios may be determined from similar types of capacitors, using e.g. simple linear alternating current (AC) transfer and nulling techniques. In one example, an AC measurement, using a sensitive lock-in amplifier, is applied. Thus, it may still be considered a challenge to calibrate the capacitances of different detector types.

<CIT> describes a method and devices for calibrating a partial discharge measuring device and for locating faults on cables. In the method, calibration signals, which can include a band-limited white noise, are used with a periodically repeated signal course. By averaging over a predetermined period duration of the calibration signal, it is possible, in the case of a partial discharge measurement, to recalibrate the measuring device continuously during the measurement, and additionally on cables to determine the fault location with great precision.

There may be a need to calibrate a capacitance ratio in an efficient and robust manner.

An attenuation measurement device and a method of deriving a capacitance ratio according to the independent claims are provided. Exemplary embodiments are described by the dependent claims.

According to an aspect of the present disclosure, there is described an attenuation measurement device, comprising:.

According to a further aspect of the present disclosure, there is described a method of operating an attenuation measurement device (as described above) having a detector unit with a coupling capacitance and an input capacitance, the method comprising:.

In the context of the present document, the term "attenuation measurement device" (in particular signal detection device) may refer to any device that is configured to receive a signal input and to produce an output associated with the input signal. In particular, a detector device may comprise a detector unit as the actual detector (for example a peak detector or an rms detector) that receives the signal and produces the corresponding output. To fulfill these objectives, the detector unit may comprise a coupling capacitance and an input capacitance. The coupling capacitance may be arranged separated from the actual detection means (e.g. the input capacitance), but may be considered as part of the detector unit. The coupling capacitance may receive an incoming (HF) signal and attenuate said signal. The attenuated signal may then be forwarded to the input capacitance, which may represent the actual detection stage. In a basic embodiment, a capacitance may be realized by a capacitor. In a more sophisticated embodiment, a capacitance may be implemented by two CMOS transistors (see e.g. <FIG>). The implementation may be for example single-ended, differential, or multi-phase.

Further, the attenuation measurement device can comprise a test unit and a calibration unit, each of which is coupled to its detector unit. In an embodiment, the test unit and the calibration unit are coupled to the detector unit, so that RF signals can still be received by the detector unit. In another embodiment, the described attenuation measurement device may be an (exact) copy of an RF signal-receiving twin (or a scaled replica of a attenuation measurement/signal detector device) and is merely configured to be used as a calibration device for the RF signal-receiving twin (or a scaled replica). Both devices may be implemented on the same chip.

In the context of the present document, the term "test signal" may particularly refer to a signal provided to a coupling (attenuation) capacitance of a detector, whereby at least one signal property of the test signal is known. The signal property may for example comprise at least one of the following: signal (power/voltage) level, signal magnitude, signal wave-shape (digital, sine-wave, etc.). The term "test unit" may refer to a hardware and/or software that is configured to produce such a test signal.

In the context of the present document, the term "calibration signal" may particularly refer to a signal that is provided to an input capacitance of a detector. The calibration signal may be essentially similar to the test signal but can also be different. In an embodiment, a plurality of calibration signals are provided to search for one specific calibration signal out of the plurality of calibration signals. The specific calibration signal may yield a comparable detector output signal as the test signal. Thereby, a capacitance-indicative information (in particular capacitance ratio/attenuation) may be derived that can be used for calibration of the detector device. The term "calibration unit" may refer to a hardware and/or software that is configured to provide such a calibration signal. Further, the calibration unit may be configured to enable an identification (e.g. by sweeping) of the specific calibration signal that is searched for.

In the context of the present document, the term "comparable" may particularly refer to the circumstance, that the detector output signals for the known test signal (at the coupling capacitance) and for the specific calibration signal (at the input capacitance) comprise comparable properties. In an embodiment, the output signals can be essentially (only unavoidable differences) similar, or even similar. In another embodiment, the output signals are on the same level or are scaled with respect to each other. In a specific embodiment (see <FIG>), the detector output voltages due to the input test signal and due to the specific calibration signal should be (essentially) equal. The skilled person will understand that there are different possibilities to implement such comparable output signals. Nevertheless, the skilled person may further understand that the comparability should be implemented such that an efficient and robust calibration of the detector device is thereby enabled. Further, "comparable" detector input signals may refer to signals having the same or approximately the same rms values, peak values, etc. of the detector, depending on the type of the detector (unit).

In the context of the present document, the term "control unit" may refer to any hardware and/or software configured to perform and/or trigger the described steps of determining, identifying, deriving (and calibrating). There are many different manners in which the control unit can be implemented. The control unit may be a single unit or a plurality of control subunits. There may be one control unit arranged in the detector unit or each unit may comprise its own control unit. For example, a part of the control unit identifies in the calibration unit, while another part derives in the detector unit. Thus, the control unit(s) can be part of the detector unit, but can also be arranged in another unit of the device or even operate remotely.

According to an exemplary embodiment, the present disclosure may be based on the idea that an efficient and robust calibration of a detector device is enabled, when a specific calibration signal applied to the detector unit input is identified, that yields a comparable detector output as a known test signal provided to a detector coupling capacitance. Based on the known test signal and the identified specific calibration signal, capacitance-indicative information, such as a coupling/input capacitance ratio and/or a coupling capacitance attenuation, may be derived that can be further used to calibrate the detector device in an efficient and robust manner.

A coupling capacitance (capacitive attenuator) may be useful to couple e.g. RF/mmWave signals (e.g. in the field of (car-related) radar) to signal detectors (in particular to the input capacitance). It may be important to know the capacitance ratio to know the signal level at the attenuator input, since the capacitance ratio may be sensitive to process variations as the two capacitances could be different types. The present disclosure describes a technique for obtaining the information based on which calibration is enabled by using (e.g. non-linear) properties of the detector unit.

In the following, further exemplary embodiments of the device and the method will be explained.

According to the invention, the calibration signal is a direct current (DC) calibration signal. Additionally the detector output signal is a DC detector output signal. Using DC instead of AC may save costs and may be more straightforward to implement. In an embodiment, only DC measurements are used to estimate the attenuation and hence the capacitance ratio. A non-linear and broadband property of the detector itself may be used hereby to estimate the capacitance ratio (using comparison/nulling technique with DC measurements).

In a further embodiment of the present disclosure, the capacitance-indicative information is derived exclusively based on DC measurements (of the output from the detector unit). Thereby, implementation, testing and energy costs may be saved, while the efficiency is not decreased and accuracy of capacitance indicative information is improved. The detector unit receives the test signal and the calibration signal as input signals and produces respective detector output signals. Hereby, both output signals (as responses to the test signal and the calibration signal) of the detector unit may be DC signals. In some implementations, there may be alternating current (AC) signals present during the detector input signal generation etc. However, the final (e.g. calibration) signal that is provided to the detector unit as an input signal is then a DC signal in this embodiment.

In a further embodiment of the present disclosure, the capacitance-indicative information comprises a capacitive ratio between the coupling capacitance and the input capacitance. In a further embodiment of the present disclosure, the capacitance-indicative information comprises a capacitive attenuation with respect to the coupling capacitance. Based on this information, the detector device may be calibrated accurately.

In a further embodiment of the present disclosure, identifying (searching for) the specific calibration signal comprises sweeping over a plurality of calibration signals. Thereby, the specific calibration signal may be found in a fast and reliable manner.

In an embodiment, the calibration unit further comprises a digital-to-analog (D/A) converter, configured to enable the sweep over the plurality of calibration signals (see the implementation in <FIG>). Here, the DC signal is generated using the digital-to-analog converter by sweeping its digital input codes.

In a further embodiment, the device comprises a polarity switch unit, configured to switch the polarity of at least one calibration signal. Thereby, a more reliable derivation of the capacitance-indicative information may be achieved.

In a further embodiment of the present disclosure, the detector is a non-linear detector, in particular it is inherent to the detector to produce comparable detector output signals in response to comparable input signals, respectively, independent of receiving the said input signals at the coupling capacitance or the input capacitance. Such a configuration of the detector may enable the calibration based on the specific calibration signal that induces a comparable detector output as the known test signal.

The disclosure may use the property of capacitive attenuators and detectors that their attenuation and response are quite broadband, respectively. The detector is typically a non-linear device which produces a (DC) response to an RF signal depending on its signal level. Due to its broadband nature, the detector produces the same (DC) output to an RF signal as a (DC) signal at the same level in an embodiment.

In a further embodiment of the present disclosure, the detector is configured to receive and detect a high frequency signal. There may be a need to attenuate such an HF signal, for which purpose the coupling capacitance may be necessary. The detector may be implemented as a peak detector and/or rms detector.

In a further embodiment of the present disclosure, providing the test signal comprises providing a clock signal. Thereby, the test signal may be provided in a reliable and cost-efficient manner. The clock signal level is well known, as it switches between the supply (vdd) and ground (vss) levels. The clock signal is sufficiently low frequent so that the transition times may be neglected compared to the rest of the clock period. Under this condition, the clock signal's rms/peak levels are known, i.e. vdd-vss, which may be measured or controlled easily. In one specific embodiment, the known test signal is a clock signal applied using CMOS inverters.

In a further embodiment of the present disclosure, the control unit is further configured to determine a test unit supply voltage, when the first detector output signal is produced in response to the test signal. Hereby, deriving the capacitance-indicative information is further based on the determined test unit supply voltage. The supply voltage of the test unit or its scaled version may be measured separately by configuring the control unit. This supply voltage vdd may then be an important parameter (specifically, it denotes the rms or peak level of the input test signal), when deriving the capacitance-indicative information.

In a specific embodiment, the capacitive attenuation (capacitance-indicative information) is measured as follows: i) A D/A-converter voltage Vdac1 is measured when the detector unit output is comparable (or same) to its response to the test signal (clock) being applied. ii) Similarly, the step is repeated with the polarity switch reversed and a voltage Vdac2 is measured. The average Vdac= (Vdac1 + Vdac2)/<NUM> is noted. The capacitive attenuation estimate is given by: Atten (dB) = <NUM>*log10 (vdd/Vdac).

In a further embodiment of the present disclosure, the coupling capacitance is coupled to the input capacitance, and the coupling capacitance is configured to provide an attenuated signal to the input capacitance. Thus, an low loss and broadband attenuation is achieved, while the capacitance ratio may be accurately measured.

In a further embodiment of the present disclosure, the input capacitance is implemented with at least two transistors, in particular two CMOS transistors.

In a further embodiment of the present disclosure, the method further comprises calibrating the detector based on the capacitance-indicative information.

In a further embodiment of the present disclosure, the method applies DC measurements, in particular exclusively DC measurements (within the detector and/or of the output from the detector unit), to derive the capacitance-indicative information.

Before referring to the drawings, exemplary embodiments will be described in further detail, some basic considerations will be summarized based on which exemplary embodiments of the present disclosure have been developed.

According to exemplary embodiments of the present disclosure, the following steps are performed:.

Thus, the present disclosure proposes a technique to measure the capacitive attenuation caused by the coupling capacitance and the input capacitance of the detector.

<FIG> illustrates an attenuation measurement device <NUM> for capacitance ratio measurement according to an exemplary embodiment. The device <NUM> comprisesa detector unit <NUM> having a coupling capacitance <NUM> (Catt) and an input capacitance <NUM> (Cdet). The detector unit <NUM> is configured to produce a detector output signal 112a,b in response to an input signal received at the coupling capacitance <NUM> and/or at the input capacitance <NUM>.

The coupling capacitance <NUM> is arranged outside of the actual detecting means (yet considered as part of the detector unit <NUM>) and receives an incoming RF signal as an input signal, whereby the incoming signal becomes attenuated by the coupling capacitance <NUM>. The input capacitance <NUM> is arranged within the actual detecting means of the detector unit <NUM> and is connected to the coupling capacitance <NUM>.

The attenuation measurement device <NUM> comprises a test unit <NUM>, coupled to the detector unit <NUM>, and configured to provide a test signal <NUM> with at least one known signal property (e.g. signal magnitude) as a first input signal to the coupling capacitance <NUM>. Further, the attenuation measurement device <NUM> comprises a calibration unit <NUM>, coupled to the detector <NUM>, and configured to provide a calibration signal <NUM> as a second input signal to the input capacitance <NUM>. In this specific embodiment, the attenuation measurement device <NUM> is a copy for calibration purposes of an actual detector device (e.g. on the same chip). Thus, the capacitances <NUM>, <NUM> are connected only to the test unit <NUM> and the calibration unit <NUM>, respectively. A switch <NUM> is provided to enable a decoupling of the calibration unit <NUM> and the capacitances <NUM>, <NUM>, so that the test signal <NUM> and the calibration signal <NUM> do not interfere.

A control unit is not shown in this example, but the control unit can be arranged anywhere in the device <NUM> or even remote. Further, the functionalities of the control unit can be split over the units <NUM>, <NUM>, <NUM> of the device <NUM>. After a test signal <NUM> is provided to the coupling capacitance <NUM> (an attenuated signal <NUM> is further directed to the input capacitance <NUM>) as a first input signal, a first detector output signal 112a (produced by the detector unit <NUM> in response to the test signal <NUM>/<NUM>) is detected. In other words, a clock is enabled, the calibration current is disabled, and the output of the detector 112a (Vdet) is measured and the supply voltage <NUM> of the inverter (vdd) is also measured. Then, it is swept over a plurality of calibration signals <NUM> to identify a specific calibration signal that yields a second detector output signal 112b that is comparable to the first detector output signal 112a. In other words, the clock is disabled, a D/A-converter code is swept such that approximately the same output value 112b (Vdet) as before is reached at the output of the detector unit <NUM>. Based on these measurements, preferably only using DC only, a capacitance-indicative information based on the identified specific calibration signal <NUM> and the known test signal <NUM> can be derived.

<FIG> illustrates a detector device <NUM> for signal detection according to another exemplary embodiment. While <FIG> shows a general embodiment, <FIG> illustrates a specific implementation in detail, wherein the attenuation measurement device <NUM> is realized in a differential CMOS design.

The detector means <NUM> are hereby implemented by using the squaring nature of MOS transistors. In particular, two transistors <NUM>, M1 and M2, form the input capacitance <NUM>. The transistor (squarer) output current is mirrored by a current mirror <NUM> and passed through a detector resistor (Rdet) to produce the detector output signals 112a,b (Vdet).

The test signal <NUM> is a clock which is made differential using inverters <NUM> and is then applied to the coupling capacitance <NUM> (coupling capacitors Catt) and the gate capacitance of the transistors <NUM> (M1, M2) that form the input capacitance <NUM>. The calibration signal <NUM> (Vdac) (and a gate bias) are applied to the detector <NUM> using further (bias) resistors <NUM> (Rgate).

Claim 1:
An attenuation measurement device (<NUM>), comprising:
a detector unit (<NUM>) having
a coupling capacitance (<NUM>), and
an input capacitance (<NUM>),
wherein the detector (<NUM>) is configured to produce a detector output signal (112a,b) in response to an input signal received at at least one of the coupling capacitance (<NUM>) and the input capacitance (<NUM>);
a test unit (<NUM>), coupled to the detector unit (<NUM>), and configured to provide a test signal (<NUM>) with at least one known signal property as a first input signal to the coupling capacitance (<NUM>);
characterized in that the detector output signal (112a, 112b) is a direct current, DC, detector output signal and in that the attenuation measurement device (<NUM>) further comprises:
a calibration unit (<NUM>), coupled to the detector unit (<NUM>), and configured to provide a calibration signal (<NUM>) as a second input signal to the input capacitance (<NUM>), wherein the calibration signal (<NUM>) is a DC calibration signal; and
a control unit configured to
determine a first detector output signal (112a) produced by the detector (<NUM>) in response to the test signal (<NUM>),
identify a specific calibration signal (<NUM>) that yields a second detector output signal (112b) that is comparable to the first detector output signal (112a), and
derive a capacitance-indicative information based on the identified specific calibration signal (<NUM>).