Generation of an RF test signal for testing an RF receiver circuit

Abstract

A circuit that features the following: an input circuit node for receiving an RF oscillator signal (s LO (t)); a first IQ modulator (111a) designed to generate a first RF signal ( SRF1 (t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a first signal (s1(t)); a second IQ modulator (111b) designed to generate a second RF signal (s RF2 (t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a second signal (s2(t)), where the first signal (s1(t)) and the second signal (s2(t)) are each complex-valued signals, each modulated by an in-phase signal component (s 1I (t), s 2I (t)) and a quadrature signal component (s 1Q (t), s 2Q (t)) are represented; and an RF combiner circuit (114) designed to generate an RF test signal (s RFTEST(t)) by combining the first RF signal ( SRF1 (t)) and the second RF signal (s RF2 (t)) to generate.

Description

TECHNICAL AREA

[0001] This description concerns the field of high-frequency (HF) circuits. Some embodiments involve a monolithic microwave integrated circuit (MMIC) with a circuit for generating test signals, which enables the testing of an HF receiver circuit contained within the MMIC. BACKGROUND

[0002] High-frequency (HF) transmitters and receivers are found in a wide variety of applications, particularly in wireless communication and radar sensors. In the automotive sector, there is a growing demand for radar sensors, which can be used in advanced driver assistance systems (ADAS) such as adaptive cruise control (ACC, or radar cruise control). These systems can automatically adjust a vehicle's speed to maintain a safe distance from other vehicles ahead (as well as other objects and pedestrians). Other automotive applications include blind spot detection, lane change assist, and similar systems.

[0003] Modern radar systems utilize highly integrated RF circuits that can combine all the core functions of a radar transceiver's RF front end in a single package (single-chip radar transceiver). Such highly integrated RF circuits are commonly referred to as monolithic microwave integrated circuits (MMICs). An RF front end typically includes (but is not necessarily required to include) a voltage-controlled oscillator (VCO) in a phase-locked loop, power amplifiers (PAs), directional couplers, mixers, and associated control circuitry for controlling and monitoring the RF front end. An MMIC may also include circuitry for analog signal processing in the baseband (or an intermediate frequency band) and analog-to-digital converters (ADCs) to enable digital signal processing.Instead of VCOs, digitally controlled oscillators (DCOs) can also be used, depending on the application. Publication US 2017 / 0082756 A1 describes a system for frequency drift compensation used in radio receivers. This system features a pilot signal generator that produces two pilot signals. These pilot signals are frequency-shifted using a mixer and a local oscillator and added to the intermediate frequency signal of the radio receiver. The frequency drift is detected based on the summed signal and then compensated for. A commercially available signal generator for producing two-tone signals is described in Application Note 1410 (titled "Two-tone and Multitone Personalities for the E8267C PSG Vector Signal Generator") by Agilent Technologies. Publication GB 2 339 917 A also describes a concept for generating a multi-tone test signal.

[0004] In sensor applications, it is often desirable or necessary to test one or more RF circuit components to ensure proper sensor operation and adherence to the required measurement accuracy. For this reason, RF circuits used in radar sensors may include components that enable one or more tests / self-tests to test and / or characterize specific RF circuit components. Publication DE 10 2015 115 017 A1 describes a radar sensor with self-test functionality. SUMMARY

[0005] The embodiments of the invention described here relate to the circuit according to claim 1, the RF (radar) receiving device according to claim 18, and the method according to claim 12. Various embodiments and further developments are the subject of the dependent claims.

[0006] The following describes a circuit which, for example, comprises: an input circuit node for receiving an RF oscillator signal; a test signal generator circuit comprising at least one modulator configured to generate an RF test signal by modulating the RF oscillator signal. The circuit further comprises at least one receive channel with a receiver circuit and a coupler configured to feed the RF test signal into the receiver circuit.

[0007] In another example, the circuit comprises the following: an input circuit node for receiving an RF oscillator signal; a first modulator configured to generate a first RF signal by modulating the RF oscillator signal with a first signal; a second modulator configured to generate a second RF signal by modulating the RF oscillator signal with a second signal. The circuit further comprises an RF combiner circuit configured to generate an RF test signal by combining the first RF signal and the second RF signal.

[0008] Furthermore, an RF receiving device is described. According to an example, the RF receiving device comprises: an antenna input for connecting an antenna; an RF signal source configured to provide an RF oscillator signal; a circuit for generating an RF test signal; a receiving mixer having an RF input and an output; and a coupler connected to the antenna input, an output of the circuit for generating the RF test signal, and the RF input of the receiving mixer, and configured to forward the RF test signal to the RF input of the receiving mixer.The circuit for generating the RF test signal comprises an input circuit node coupled to the RF signal source to receive the RF oscillator signal, a first modulator configured to generate a first RF signal by modulating the RF oscillator signal with a second signal, and a second modulator configured to generate a second RF signal by modulating the RF oscillator signal with a second signal. An RF combiner circuit is configured to generate an RF test signal by combining the first and second RF signals.

[0009] Furthermore, a method is described which includes the following: generating an RF test signal by modulating several modulation signals onto a high-frequency signal, and feeding the RF test signal into at least one RF circuit.

[0010] According to another example, the method comprises generating a first RF signal by modulating an RF oscillator signal with a first signal, and generating a second RF signal by modulating the RF oscillator signal with a second signal. The method further comprises generating an RF test signal by combining the first RF signal and the second RF signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The following illustrations explain exemplary embodiments in more detail. The illustrations are not necessarily to scale, and the exemplary embodiments are not limited to the aspects shown. Rather, the emphasis is placed on illustrating the underlying principles of the exemplary embodiments. The illustrations show: Fig. Figure 1 is a sketch illustrating the operating principle of an FMCW radar system for distance and / or speed measurement. Fig. 2 includes two timing diagrams to illustrate the frequency modulation of the RF signal generated by the FMCW system. Fig. Figure 3 is a block diagram illustrating the basic structure of an FMCW radar system. Fig. Figure 4 is a block diagram illustrating an exemplary implementation of a transmit channel and a receive channel of a radar system. Fig. Figure 5 is a block diagram illustrating an example of a radar system receiving channel with an additional RF test signal generator circuit that enables testing of the receiver circuit contained in the RF front end. Fig. Figure 6 illustrates exemplary spectra of single-tone and two-tone signals used as test signals in the example from Fig. 5 occur. Fig. Figure 7 is a block diagram of an exemplary embodiment of an improved test signal generator circuit, which in the example is from Fig. 5 can be used. Fig. Figure 8 illustrates an exemplary implementation of the embodiment from Fig. 7. Fig. Figure 9 illustrates exemplary spectra of single-tone and two-tone signals used as test signals in the examples from Fig. 7 or Fig. 8 can occur. Fig. Figure 10 illustrates exemplary spectra of single-tone signals with different phases, which are used as test signals in the examples from Fig. 7 or Fig. 8 can occur. Fig. Figure 11 is a flowchart illustrating an embodiment of a method for generating an RF test signal for testing an RF receiver circuit. Fig. Figure 12 is a flowchart illustrating an embodiment of a method for quantitatively testing an RF receiver circuit with an RF test signal. DETAILED DESCRIPTION

[0012] The embodiments described here are presented in the context of a radar receiver or transceiver. However, the various embodiments described here are not limited to radar applications and can also be used in other areas, for example in RF transceivers of RF communication devices.

[0013] Fig. Figure 1 illustrates the application of an FMCW radar system as a sensor for measuring the distances and velocities of objects commonly referred to as radar targets. In this example, the radar device has 10 separate transmit (TX) and receive (RX) antennas 5 and 6, respectively (bistastatic or pseudo-monostatic radar configuration). However, it should be noted that a single antenna can also be used, serving simultaneously as both a transmit and receive antenna (monostatic radar configuration). The transmit antenna 5 radiates a continuous RF signal s RF (t) ab, which is frequency-modulated, for example, with a linear chirp signal (periodic, linear frequency ramp). The radiated signal s RF (t) is backscattered at radar target T and the backscattered (reflected) signal y RF (t) is received by the receiving antenna 6.

[0014] Fig. Figure 2 illustrates, by way of example, the aforementioned frequency modulation of the signal s RF (t). As in Fig. The signal shown in 2 is s RF (t) composed of a set of “chirps”, i.e., signal s RF (t) comprises a sequence of sinusoidal waveforms with increasing (up-chirp) or decreasing (down-chirp) frequency (see upper diagram in Fig. 2) In the present example, the instantaneous frequency f(t) of a chirp increases at a starting frequency f. START beginning within a time period T RAMP linearly to a stopping frequency f STOP an (see lower diagram in Fig. 2) Such chirps are also referred to as a linear frequency ramp. In Fig. Figure 2 shows three identical linear frequency ramps. It should be noted, however, that the parameters f START , f STOP , T RAMPThe pause between individual frequency ramps can also vary. Furthermore, the frequency variation does not necessarily have to be linear. Depending on the implementation, for example, transmission signals with exponential (exponential chirps) or hyperbolic (hyperbolic chirps) frequency variation can be used.

[0015] Fig. Figure 3 is a block diagram illustrating a possible structure of a radar device 1 (radar sensor). Similar structures can also be found, for example, in RF transceivers used in other applications, such as wireless communication systems. Accordingly, at least one transmit antenna 5 (TX antenna) and at least one receive antenna 6 (RX antenna) are connected to an RF front end 10, which can include all the circuit components required for RF signal processing. These circuit components include, for example, a local oscillator (LO), RF power amplifiers, low-noise amplifiers (LNAs), directional couplers (e.g., rat-race couplers, circulators, etc.), and mixers for downconverting the RF signals to the baseband or an intermediate frequency (IF) band. The RF front end 10 can – if necessary –together with other circuit components, it can be integrated into a monolithic microwave integrated circuit (MMIC). The example shown depicts a bistatic (or pseudo-monostatic) radar system with separate RX and TX antennas. In the case of a monostatic radar system, a single antenna would be used for both transmitting and receiving the electromagnetic (radar) signals. In this case, a directional coupler (e.g., a circulator) can be used to separate the RF signals transmitted into the radar channel from the RF signals (radar echoes) received by the radar channel. In practice, radar systems usually have multiple transmit and receive channels with multiple transmit and receive antennas, respectively, which, among other things, allows for the measurement of the direction (DoA, direction of arrival) from which the radar echoes are received.

[0016] In the case of a frequency-modulated continuous-wave radar system (FMCW radar system), the RF signals radiated via the TX antenna 5 can be in the range of approximately 20 GHz to 100 GHz (e.g., around 77 GHz in some applications). As mentioned, the RF signal received by the RX antenna 6 includes the radar echoes, i.e., those signal components that are backscattered from one or more radar targets. The received RF signal y RF (t) is, for example, downmixed to the baseband and further processed in the baseband using analog signal processing (see Fig. 3. Analog baseband signal processing chain 20). The aforementioned analog signal processing essentially comprises filtering and, if necessary, amplification of the baseband signal. The baseband signal is then digitized (see Fig. 3, Analog-to-Digital Converter 30) and further processed in the digital domain. The digital signal processing chain can be implemented, at least partially, as software running on a processor, for example a microcontroller or a digital signal processor (see Fig. 3, DSP 40). The overall system is typically controlled by a system controller 50, which can also be implemented, at least partially, as software running on a processor such as a microcontroller. The RF front end 10 and the analog baseband signal processing chain 20 (optionally also the analog-to-digital converter 30) can be integrated together in a single MMIC (i.e., an RF semiconductor chip). Alternatively, the individual components can also be distributed across several integrated circuits.

[0017] Fig. Figure 4 illustrates an exemplary implementation of the RF frontend 10 with downstream baseband signal processing chain 20, which is part of the radar sensor. Fig. There can be 3. It should be noted that Fig. Figure 4 shows a simplified circuit diagram to illustrate the basic structure of the RF front end with one transmit channel (TX channel TX01) and one receive channel (RX channel RX01). Actual implementations, which can vary significantly depending on the specific application, are naturally more complex and typically feature multiple TX and / or RX channels. The RF front end 10 includes a local oscillator 101 (LO), which generates an RF oscillator signal s LO (t) is generated. The RF oscillator signal s LO (t) can, as above with reference to Fig. As described in section 2, the LO signal is frequency-modulated and is also referred to as the LO signal. In radar applications, the LO signal is typically in the SHF (Super High Frequency, centimeter wave) or EHF (Extremely High Frequency, millimeter wave) band, e.g., in the interval from 76 GHz to 81 GHz in some automotive applications.

[0018] The LO signal s LO (t) is processed in both the transmit signal path (in the TX channel) and the receive signal path (in the RX channel). The transmit signal s RF (t) (cf. Fig. 2), which is radiated from the TX antenna 5, is amplified by amplifying the LO signal s LO (t), for example by means of the RF power amplifier 102, is generated and is therefore merely an amplified version of the LO signal s LO (t). The output of amplifier 102 can be coupled to the TX antenna 5 (in the case of a bisstatic or pseudo-monostatic radar configuration). The received signal y RF(t), which is received by the RX antenna 6, is fed to the receiver circuit in the RX channel and thus directly or indirectly to the RF port of the mixer 104. The receive signal path (the RX channel) essentially comprises a heterodyne receiver. In the present example, the RF receive signal y RF (t) (antenna signal) is pre-amplified by amplifier 103 (gain g). The amplified RF receive signal gy is then fed to mixer 104. RF (t) supplied. Amplifier 103 can be, for example, an LNA. The LO signal s is supplied to the reference port of mixer 104. LO (t) supplied, so that the mixer 104 receives the (pre-amplified) RF receive signal y RF (t) downmixes to the baseband. The downmixed baseband signal (mixer output signal) is then used with y BB (t) denotes this baseband signal y. BB(t) is first processed further in an analog manner, whereby the analog baseband signal processing chain 20 can essentially include amplification (amplifier 22) and filtering (e.g., bandpass 21) to suppress unwanted sidebands and image frequencies. The resulting analog output signal, which is fed to an analog-to-digital converter (see Fig. The signal that can be fed to the ADC 30 (3) is denoted by y(t). Methods for the digital processing of the output signal (digital radar signal) are known per se (for example, range Doppler analysis) and are therefore not discussed further here.

[0019] In the present example, mixer 104 mixes the pre-amplified RF receive signal g·y RF(t) (i.e., the amplified antenna signal) down to the baseband. The mixing can be done in one stage (i.e., from the RF band directly to the baseband) or via one or more intermediate stages (i.e., from the RF band to an intermediate frequency band and then to the baseband). In this case, the receive mixer 104 effectively comprises several individual mixer stages connected in series. Given the in Fig. The example shown in section 4 clearly demonstrates that the quality of a radar measurement depends heavily on the quality of the LO signal. LO (t) as well as depends on the linearity of the circuit components arranged in the receive signal path. For example, the linearity of the receive mixer 104 is a relevant parameter.

[0020] Nonlinearity in the receiver mixer 104 leads to intermodulation distortion of the radar signals. The linearity (or nonlinearity) of a circuit component such as the receiver mixer 104 can be quantitatively characterized by measuring the properties (amplitude, power, etc.) of intermodulation products (IMPs). For example, if the power of IMPs is below a specifiable threshold, the tested circuit component (or signal path) can be considered sufficiently linear (for the respective application). In radar applications, distortions caused by intermodulation from IMPs can negatively affect the measurement result, thus degrading the accuracy and reliability of the radar measurements.To characterize the linearity of the receive channels, an MMIC can include circuit components that allow information about linearity to be determined during a test and / or a self-test. Such a test could be, for example, an end-of-line test (EOL test, automated test towards the end of production) or a self-test performed during operation of the MMIC.

[0021] Fig. Figure 5 is a block diagram showing a receiver circuit of a receiving channel RX01 of an RF transceiver, which corresponds to the example from Fig. 4 is similar, but with additional circuitry that enables the tests mentioned above. The RF receiver circuit is an RF input signal y RF (t) supplied, which was received, for example, by means of an antenna (not shown). During a test, this signal can be zero (y). RF (t)=0V), which results in interference-free operation. The RF input signal y RF(t) is routed to mixer 104 via directional coupler 110. As in the example from Fig. 1 can be the RF input signal y RF (t) are pre-amplified, with the amplifier 103 being connected upstream or downstream of the directional coupler 15. In the present example, the amplifier 103 is connected between the directional coupler 110 and the mixer 104. The signal processing chain following the mixer 104 is the same as in the example according to Fig. 4. Accordingly, the output of mixer 104 is coupled to the input of the analog baseband signal processing chain 20, which suppresses, in particular, unwanted sidebands and image frequencies in the output signal of mixer 104. The output of the analog baseband signal processing chain 20 is coupled to an analog input of the analog-to-digital converter 30, which is configured to digitize the preprocessed baseband signal y(t). The digital representation of the preprocessed baseband signal y(t) is denoted by y[n] and can be further processed by the signal processor 40. The signal processing chain from the directional coupler 110 to the analog-to-digital converter 30 is also referred to as the receiver circuit or receive channel. As mentioned, real radar systems typically have several receive channels.

[0022] The directional coupler 110 enables the coupling of an RF test signal. RFTEST(t) into the receive signal path of RX channel RX01, thereby transmitting the RF test signal s RFTEST (t) is fed to the RF port (RF gate) of mixer 104 (e.g. as an alternative to the input signal y) RF (t)). The RF test signal s RFTEST (t) can be like the RF input signal y RF (t) are pre-amplified by means of amplifier 103. The directional coupler 110 can, for example, be a ring coupler implemented using strip lines. As is typical for such couplers, one port is terminated by means of a terminating impedance 16. Alternatively, the coupler 110 can be a passive or an active circulator. Other types of couplers can also be used. As mentioned, the receiving mixer 104 can also be constructed from a series connection of several mixer stages.

[0023] Essentially, the RF test signal s RFTEST(t) is “injected” into the receive signal path of RX channel RX01, and mixer 104 consequently “sees” the RF test signal s RFTEST (t) like a regular RF input signal. The RF test signal s RFTEST (t) can therefore also be referred to as a "virtual radar echo". In the example shown, the RF test signal s RFTEST (t) is generated by a test signal generator circuit TSG. This contains a modulator 111, which generates the LO signal s LO (t) (e.g. generated by a local oscillator in the chip or supplied via an external pin), which has a carrier frequency f LO exhibits, with a test signal s TEST (t) (modulation signal) is modulated. The test signal s TEST (t) can be, for example, a single-tone signal that only has a single frequency f TESTIn practice, a single-tone signal is a very narrowband signal that essentially has only one spectral line (frequency bin). A "tone" is generally understood to be a sine wave with a specific frequency and phase. Several tones can be superimposed to form an N-tone signal, where N denotes the number of tones. In the embodiments described here, narrowband modulation signals with non-overlapping frequency bands can be used instead of single-tone signals. In this context, narrowband means that the modulation signals have a defined bandwidth greater than zero and thus encompass more than a single tone. The spectrum of the modulation signals can be continuous (within the considered frequency band) or consist of several discrete frequencies.

[0024] Under ideal conditions, the baseband signal y(t), and therefore also the digital radar signal y[n], should again be a single-tone signal; mixer 104 performs a demodulation that reverses the modulation effected by modulator 111. However, a (slight) nonlinearity in the receive signal path (e.g., in mixer 104) leads to harmonic distortion, and the digital radar signal y[n] is distorted in addition to the frequency f. TEST also exhibit high harmonics, i.e., integer multiples of the frequency f TESTFor some tests, two-tone signals or, more generally, N-tone signals are required, which exhibit two or more frequencies or spectral lines. This is particularly the case when not only the function of the received signal path (receiver circuitry of an RX channel) is to be tested, but also its linearity / nonlinearity is to be quantitatively determined. If the test signal has two or more tones (sine waves), in addition to harmonic distortion, the aforementioned intermodulation distortions also occur, which will be discussed in more detail below (see below). Fig. 6) The test signal S TESTThe modulation signal can be generated, for example, using a direct digital synthesizer (DDS), which is a type of frequency synthesizer that can be used to generate any signal waveform. Other types of signal sources can also be used. Instead of using a DDS, it is also possible, for example in an end-of-life (EOL) test, to generate the test signal s TEST (t) to be generated by an external device (e.g., an automatic test system, ATE) and fed into the MMIC via an external pin or test pad. In this case, only modulator 111 is required from the test signal generator circuit TSG.

[0025] The in Fig. The test signal generator circuit TSG shown in Figure 5 is suitable for testing the function of the circuit components arranged in an RX channel. The test can be repeated for several or all RX channels of a radar system. As shown below, Fig. As explained in section 6, this is the one in Fig. The test signal generator circuit TSG shown in Figure 5 is not readily suitable for quantitatively determining the linearity of the receiver circuit of an RX channel, i.e., for measuring the distortions caused by nonlinearities. A possible measurement for linearity would be, for example, the ratio of the power of all intermodulation products (IMPs) to the power of the test signal. TEST (t). For a quantitative characterization of the linearity, the RF test signal s should be used. RFTEST (t) a high-quality two-tone signal or N-tone signal (frequency shifted by the carrier frequency f) LO ). However, even in the (theoretical) case that the signal s TEST (t) is a perfect two-tone signal, the RF test signal s RFTEST(t) already contain IMPs and harmonics, and it is no longer possible to distinguish during measurement whether the IMPs in the analog and digital radar signals y(t) and y[n] are generated by the modulator 111 or the receiver mixer 104. The modulator 111 should therefore exhibit comparatively high linearity. Since the linearity of the modulator 111 in a realistic implementation in an MMIC is usually not significantly better than the linearity of the receiver mixer 104, the simple test signal generator circuit TSG from Fig. 5 is not readily suitable for a quantitative characterization of the linearity of an RF receiver circuit integrated in an MMIC.

[0026] Fig. Figure 6 illustrates, using exemplary spectra, the detection of IMPs in the output signal of a receiver circuit (analog or digital radar signal y(t) or y[n]) and the determination of the power of the IMPs. Diagram (a) of the Fig. Figure 6 illustrates the spectrum of a two-tone signal as an example of a test signal. TEST (t); the spectrum essentially comprises two spectral lines, one at frequency f1 and one at frequency f2. This test signal s TEST (t) is, as explained above, by modulator 111 (see above). Fig. 5) transformed into the RF range and the resulting RF test signal s RFTEST (t) into a receiving channel (see Fig. 5, RX channel RX01) is fed in and mixed back into the baseband via the receive mixer 104. The spectrum of the resulting output signal y[n] of the receive channel is shown as an example in diagram (a) of the Fig. Figure 6 illustrates this. Accordingly, the spectrum of the resulting baseband signal also includes the two spectral lines at frequencies f1 and f2, but additionally also further spectral lines of the higher harmonics and the intermodulation products (IMPs). As mentioned above, instead of the single-tone signals at frequencies f1 and f2, more or less narrowband modulation signals can also be used, exhibiting non-overlapping frequency bands (e.g., with f1 and f2 as center frequencies) of finite bandwidth.

[0027] The additional spectral lines due to harmonic distortions lie at integer multiples of the frequencies f1 and f2, i.e., at m·f1 and n·f2 (m,n = 2, 3, 4, ...). The additional spectral lines of the IMPs lie at the sums of integer multiples of the frequencies f1 and f2, i.e., at k·f1 + l·f2 (k = ±1, ±2, ±3, ..., and l = ±1, ±2, ±3, ...). Since the factors k and l can also be negative, the aforementioned sums also include the differences of integer multiples of the frequencies f1 and f2. The power of the spectral lines at the frequencies k·f1 + l·f2 relative to the power of the two-tone signal (diagram (a) of the Fig. 6) can be used as a measure of the linearity of the receiver circuit of the respective receiving channel, with the linearity being greater the smaller the power of the intermodulation products and the higher harmonics.

[0028] The power of the intermodulation products can therefore be used as a measure of linearity. In the case of the Fig. However, in the example shown (5), the problem is that the two-tone test signal s TEST (t) is transformed into the RF range by converting the LO signal s LO (t) with the test signal s TEST (t) is modulated (see Fig. 5, Modulator 111). However, Modulator 111 itself causes IMPs, and therefore one can use the measured spectrum (see Fig. 6, Diagram (b)) no longer clearly determines whether the IMPs are actually caused by the receiver circuit (e.g., mixer 104) or were already caused by modulator 111. For this reason, the circuit from Fig. Although signal 5 can be used to test the function of the receiver circuit in RX channel RX01 itself, it is not suitable for a quantitative determination of the linearity of the receiver circuit (mixer 104). A high-quality RF test signal would be required for a quantitative determination. RFTEST (t) is required, which has no IMPs, so that the IMPs detected in the spectrum can be clearly attributed to the receiver circuit.

[0029] Fig. Figure 7 shows an example of an improved test signal generator circuit (TSG) used in an MMIC instead of the one in Fig. The circuit shown in Figure 5 can be used to generate an RF test signal. As shown in Figure 5. Fig. As shown in Figure 7, the test signal generator circuit TSG can have two signal sources, SQ1 and SQ2, whose output signals are labeled s1(t) and s2(t), respectively. If an N-tone signal is to be generated instead of a two-tone signal, more than two signal sources can be provided. In the example shown, the signal sources SQ1 and SQ2 are located in the same MMIC as the RX channel RX01. For an end-of-line (EOL) test, however, the signals s1(t) and s2(t) can also be generated in an external test setup and fed into the MMIC via pins or test pads.

[0030] In the Fig. In the example shown, signal sources SQ1 and SQ2 each comprise a digital signal generator (DSG) 112a and 112b, respectively, and an analog-to-digital converter 113a, 113b. The output signal of the first signal generator 112a is denoted by s1[n] and the output signal of the second signal generator 112a by s1[n]. The digital signals s1[n] and s2[n] are converted by the analog-to-digital converters 113a and 113b, respectively, into the analog signals s1(t) and s2(t), which are available at the outputs of signal sources SQ1 and SQ2, respectively. Alternatively, analog signal generation is also possible. Regardless of the implementation of the signal sources SQ1 and SQ2, the output signals of the two (or more) signal sources SQ1 and SQ2 are each single-tone signals that differ in their frequency or phase (or in frequency and phase).

[0031] The test signal generator circuit TSG has a modulator for each signal source SQ1 and SQ2. In the case of two single-tone signals s1(t) and s2(t), a first modulator 111a is connected to the first signal source SQ1, and a second modulator 111b is connected to the second signal source SQ2. In examples with more than two signal sources, correspondingly more than two modulators are provided. The modulators 111a and 111b are configured to generate an RF oscillator signal, such as the LO signal s. LO (t) to modulate with the output signals s1(t) and s2(t) of the signal sources SQ1 and SQ2. The resulting modulated RF signals are denoted by s RF1 (t) and S RF2 (t) denotes the two RF signals s RF1 (t) and S RF2(t) are fed to an RF combiner circuit 114, which can be implemented, for example, as a Wilkinson power combiner. Other active or passive implementations of the RF combiner circuit 114 are possible. According to one embodiment, the RF combiner circuit 114 is configured to output an RF test signal s at its output. RFTEST (t) a linear combination of the two RF signals s RF1 (t) and S RF2 (t) to provide. In this case, the RF test signal would be s RFTEST (t) equals g1 · s RF1 (t) + g2 · s RF2 (t), where the factors g1 and g2 denote gains which are usually equal (g1=g2) and can also be less than one.

[0032] Unlike in the example from Fig. 5. Two modulators are used to generate an RF test signal modulated with a two-tone signal, which modulate the RF oscillator signal s LO(t) each with a single-tone signal (signals s1(t) and s2(t)). In the case of an N-tone signal, N modulators are used to generate N RF signals modulated by a single-tone signal each. The use of multiple modulators, each fed a single-tone signal as a modulation signal, has the effect that harmonic distortions occur in the modulators, but no intermodulation distortions. However, even if, for example, instead of four single-tone signals and four modulators, only two two-tone signals and two modulators were used to modulate the RF oscillator signal with four tones, an improvement (a reduction in IMPs) can be achieved compared to the case in which only one modulator is used. If in the spectrum of the output signal to be determined (see e.g. Fig. 5, Signal y[n]) nevertheless IMPs occur, these can be clearly assigned to the receiver circuit of the respective receiving channel, in particular to the respective receiving mixer.

[0033] Fig. Figure 8 shows another example of an improved test signal generator circuit (TSG). In the example shown, the signals s1(t) and s2(t) generated by the signal sources SQ1 and SQ2 are complex-valued signals. That is, s1(t) = s1(t) + j·s Q1 (t) and s2(t) = s I2 (t) + j · s Q2 (t), where the signal components s I1 (t) and s I2 (t) as in-phase components (in-phase signals) and the signal components s Q1 (t) and s Q2(t) are referred to as quadrature components (quadrature signals) (j denotes the imaginary unit). In this case as well, the signals s1(t) and s2(t) are single-tone signals and generally have the form s1(t) = A1·exp(j·2πf1·t) and s2(t) = A2·exp(j·2πf2·t), respectively, where A1 and A2 denote the signal amplitudes and exp(·) the natural exponential function. In the case of a digital implementation of the signal sources SQ1 and SQ2, these can each have two analog-to-digital converters 113a, 113a' and 113b, 113b' (or one analog-to-digital converter with two channels each) to process both the digital in-phase signal components s I1 [n] and s I2[ n] as well as the digital quadrature signal components in s Q1 [n] and s Q2 [n] to convert into analog signals. Analog and digital signal generators designed to generate complex-valued single-tone signals are known per se and are therefore not explained in detail here.

[0034] In an implementation with complex-valued single-tone signals s1(t) and s2(t), the corresponding modulators 111a and 111b can be implemented as IQ modulators. IQ modulators (IQM) are well-known and therefore will not be discussed further here. IQ modulators are also known by other names such as quadrature modulators, quadrature upconverters, Cartesian upconverters, etc. Essentially, the IQ modulators effect single-sideband modulation of the LO signal s. LO (t). As in the previous example from Fig. 7 the output signals s RF1 (t) and s RF2 (t) the modulators 111a and 111b are combined by means of an RF combiner circuit 114, which in turn can be configured as a Wilkinson power combiner.

[0035] In this case, the output signal is s RFTEST (t) of the RF combiner circuit 114 a linear combination of the RF signals s RF1 (t) and s RF2(t). Since the IQ modulators 111a and 111b are supplied with single-tone signals (complex-valued) as modulation signals, only higher harmonics are generated, but no IMPs. The combined signal s RFTEST (t) contains no IMPs.

[0036] As mentioned, the separate modulation of the RF oscillator signal s LO (t) with two or more single-tone signals and the subsequent (linear) combination of the modulated RF signals has the effect that in the RF test signal s RFTEST (t) no IMPs are present. Therefore, IMPs that are in the spectrum of the output signal y[n] of a receiving channel (cf. Fig. 5, RX channel RX01) can be clearly attributed to the respective receiver circuit of the receiving channel. This fact is described in the Fig. The spectra shown in Figure 9 are exemplary. The third (lower) diagram shows the spectrum of the output signal y[n] of an RX channel in the (theoretical) case of perfect linearity of the receiver circuit, so that no IMPs occur. The higher harmonics are already caused by harmonic distortions in modulators 111a and 111b of the test signal generator circuit TSG. Unlike in the Fig. In the case shown in section 6, no IMPs are generated in the test signal generator circuit TSG because a separate modulator is provided for each individual tone signal. The first (upper) diagram of the Fig. Figure 9 shows the part of the spectrum that can be attributed to the first single-tone signal s1(t) with frequency f1; the second (middle) diagram of the Fig. Figure 9 shows the part of the spectrum that can be attributed to the first single-tone signal s2(t) with frequency f2.

[0037] If the spectrum of the output signal y[n] of an RX channel (see the lower diagram of the Fig. 9) If IMPs occur, they could be clearly attributed to a nonlinearity in the receiver circuit of the respective RX channel, thus enabling a quantitative measurement of the linearity of the receiver circuit. Since the RF test signal does not contain any (due to modulation around the frequency f) LO Since the spectrum contains shifted spectral lines at the frequencies k·f1 + l·f2 for k≠0 and l≠0 (k and l are integers) – that is, no IMPs – any IMPs that may occur must be generated by a nonlinearity in the receiver circuit, for example, the receive mixer 104. In general terms, spectral lines (e.g., due to IMPs) in the spectrum of the output signal y[n] of an RX channel that have no correspondence (i.e., no corresponding spectral line) in the RF test signal s RFTEST (t) originate from nonlinearities in the receiver circuit of the channel in question.

[0038] Fig. Figure 10 illustrates, using the resulting spectra, another alternative for generating an RF test signal, which is shown in the examples from Fig. 7 and Fig. 8 can be used. As in the previous example from Fig. Figure 9 shows the first (top) diagram of the Fig. 10 that part of the spectrum which is attributable to the first single-tone signal s1(t) with frequency f1, and the second (middle) diagram of the Fig. Figure 10 shows the part of the spectrum attributable to the first single-tone signal s2(t) with frequency f2. The third (lower) diagram shows the spectrum of the output signal y[n] of an RX channel in the (theoretical) case of perfect linearity of the receiver circuit, so that no IMPs occur.

[0039] Unlike the previous case, in the example shown, the two frequencies f1 and f2 are equal (f1=f2). However, the two individual tone signals s1(t) and s2(t) differ in phase, where the phase difference φ 2,1 -φ 1,1 The fundamental frequency is 90° (i.e., n / 2) or an odd multiple thereof. In the example shown, the phase φ is 1,1 of the first signal s1(t) 0° and the phase φ 2,1 of the second signal s2(t) 90°. The phases φ 2,2 , φ 2,3 The higher harmonics 2·f2, 3·f2, etc., generated in modulators 111a and 111b, are multiplied accordingly. The phase of the first harmonic 2·f2 (=2·f1) is therefore 180°, which is why, when superimposed in the RF combiner circuit 114 (see... Fig. 7 or Fig. 8) destructive interference occurs. The resulting RF test signal s RFTEST(t) in the present example is not a two-tone signal, but a single-tone signal with frequency f1=f2; however, the use of two separate modulators ensures that in the RF test signal s RFTEST (t) the second harmonic is canceled out at the frequency 2·f2.

[0040] If, now, in the spectrum of the output signal y[n] of an RX channel (see the lower diagram of the Fig. 10) If a spectral line were nevertheless to appear at the frequency 2·f1, it could be clearly attributed to a nonlinearity in the receiver circuit of the respective RX channel. In this case, too, a quantitative measurement of the linearity of the receiver circuit is possible, since the signal power of the first harmonic can be used as a measure of the linearity or nonlinearity of the receiver circuit of the channel in question, because the spectral line at the frequency 2·f1 has no equivalent (i.e., no corresponding spectral line) in the RF test signal sRFTEST (t) has.

[0041] Fig. 11 and Fig. Figure 12 are flowcharts illustrating an example of a procedure for generating a high-quality RF test signal (i.e., essentially without significant IMPs) in an MMIC for testing one or more receiver circuits of one or more RX channels of the MMIC. Fig. Figure 11 illustrates the generation of the test signal and Fig. 12. Testing a receiver circuit integrated into the MMIC. In the example shown, the procedure (step S1) includes generating an initial RF signal (see e.g. Fig. 7, RF signal s RF1 (t)) by modulating an RF oscillator signal (see e.g. Fig. 5 and Fig. 7, LO signal s LO (t)) with a first single tone signal (see e.g. Fig. 7, signal s1(t) with frequency f1 and phase φ1) and (step S2) the generation of a second RF signal (see e.g. Fig. 7, RF signal s RF2(t)) by modulating the RF oscillator signal with a second single-tone signal (see e.g. Fig. 7. Signals s2(t) with frequency f2 and phase φ2). The individual tone signals differ in their frequency or in their phase or in both (f1≠f2 and / or φ1≠φ2). An RF test signal (see e.g. Fig. 7, RF test signal s RFTEST (t)) is generated (step S3) by combining the first RF signal and the second RF signal, which largely prevents the formation of IMPs.

[0042] As mentioned, the two single-tone signals can be generated by signal sources integrated into the MMIC (see Fig. 7 and Fig. 8, signal sources SQ1 and SQ2) or are generated in an external test setup and fed into the MMIC. The RF test signal is then fed into the receiver circuit, for example via a coupler, so that it is supplied to the RF input of the receiver mixer (see e.g. Fig. 5, coupler 110, receiver mixer 104). The receiver mixer downmixes the RF test signal to the baseband (see Fig. 12, step S4). The baseband signal (e.g., further processed analogously) can be considered the output signal of the receiver circuit (see Fig. 5, Signal y(t)); this output signal is digitized (see below). Fig. 5, digital output signal y[n]), which enables further digital processing (see Fig.12, Step S5). The digital processing consists of a spectral analysis of the digitized signal, whereby at least a portion of the spectrum is calculated (e.g., a power spectral density). Within this spectrum, those spectral lines can be detected that have no corresponding spectral line in the RF test signal. These detected spectral lines can be attributed to a nonlinearity in the receiver circuit. The power of these spectral lines can also be used as a measure of the linearity of the receiver circuit, particularly the receiving mixer, with the linearity being higher the lower the power or amplitude of the detected spectral lines that have no corresponding line in the RF test signal.

Claims

[1] A circuit which has the following features: an input circuit node for receiving an RF oscillator signal (s LO (t)); a first IQ modulator (111a) designed to generate a first RF signal ( SRF1 (t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a first signal (s1(t)); a second IQ modulator (111b) designed to generate a second RF signal (s RF2 (t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a second signal (s2(t)), where the first signal (s1(t)) and the second signal (s2(t)) are each complex-valued signals, each modulated by an in-phase signal component (s 1I (t), s 2I (t)) and a quadrature signal component (s 1Q (t), s 2Q (t)) are represented; and an RF combiner circuit (114) designed to generate an RF test signal (s RFTEST(t)) by combining the first RF signal ( SRF1 (t)) and the second RF signal (s RF2 (t)) to generate. [2] The circuit according to claim 1, wherein the first signal (s1(t)) and the second signal (s2(t)) are single-tone signals that differ in their frequency and / or in their phase. [3] The circuit according to claim 1, further comprising: a signal source designed to generate the first signal (s1(t)) and the second signal (s2(t)), where the first signal (s1(t)) and the second signal (s2(t)) each have essentially a single frequency (f1, f2) and a phase (φ1, φ2). [4] The circuit according to claim 3, wherein the first signal source comprises: comprising a first digital signal generator (112a) and a downstream first digital-to-analog converter (113a) configured to provide the first signal (s1(t)) as an output signal; and comprising a second digital signal generator (112b) and a downstream second digital / analog converter (113b) configured to provide the second signal (s1(t)) as an output signal. [5] The circuit according to any one of claims 1 to 4, further comprising: an RF receiving circuit with a receiving mixer (104) and a coupler (110) connected upstream of the receiving mixer (104), which is configured to receive the RF test signal (s RFTEST (t)) to receive and forward to an RF input of the receiving mixer (104). [6] The circuit according to claim 5, wherein the RF receiving circuit further comprises: an analog-to-digital converter (30) coupled to an output of the receiving mixer (104) and configured to digitize an output signal of the receiving mixer (104) and to generate a corresponding digital signal (y[n]). [7] The circuit according to claim 6, which further comprises: a processor (40) coupled to the analog-to-digital converter (30) and designed to calculate at least a part of the spectrum of the digital signal (y[n]). [8] The circuit according to claim 7, wherein the processor (40) is further configured to provide information relating to the linearity of the RF receiving circuit based on the spectrum of the digital signal (y[n]). [9] The circuit according to claim 8, wherein the RF receiving circuit further comprises: an RF amplifier (103) which is connected between the coupler (110) and the receiver mixer (104), the information concerning the linearity of the RF receiving circuit includes information about the linearity of the combination of the RF amplifier (103) and receiving mixer. [10] The circuit according to claim 8 or 9, wherein the information relating to the linearity of the RF receiving circuit includes information about spectral lines of the digital signal (y[n]) that have no corresponding value in the RF test signal (s RFTEST (t)) have. [11] The circuit according to any one of claims 1 to 10, where the first RF signal ( SRF1 (t)) exhibits spectral lines that correspond to integer multiples of the frequency of the first signal (s1(t)) and are offset by the frequency of the RF oscillator signal (s LO (t)) are shifted and, where the second RF signal (s RF2 (t)) exhibits spectral lines that correspond to integer multiples of the frequency of the second signal (s2(t)) and are offset by the frequency of the RF oscillator signal (s LO (t)) are shifted and, and where the first RF signal ( SRF1 (t)) and the second RF signal (s RF2(t)) does not exhibit any spectral lines corresponding to sums and / or differences of integer multiples of the frequency of the first signal (s1(t)) and the frequency of the second signal (s2(t)) and around the frequency of the RF oscillator signal (s LO (t)) are shifted. [12] A procedure that includes: Generating a first signal (s1(t)) and a second signal (s2(t)) as complex-valued signals, each separated by an in-phase signal component (s 1I (t), s 2I (t)) and a quadrature signal component (s 1Q (t), s 2Q (t)) are represented; Generating an initial RF signal ( SRF1 (t)) by modulating an RF oscillator signal (s LO (t)) with the first signal (s1(t)) using a first IQ modulator (111a); Generating a second RF signal (s RF2 (t)) by modulating the RF oscillator signal (s LO(t)) with the second signal (s2(t)) by means of a second IQ modulator (111b), ; and Generating an RF test signal (s RFTEST (t)) by combining the first RF signal ( SRF1 (t)) and the second RF signal (s RF2 (t)). [13] The method according to claim 12, wherein the first signal (s1(t)) and the second signal (s2(t)) are single-tone signals that differ in their frequency and / or in their phase. [14] The method according to claim 12 or 13, further comprising: Coupling of the RF test signal (s RFTEST (t)) into an RF receiving circuit with a receiving mixer (104) such that the RF test signal (s RFTEST (t)) is fed to an input of the receiving mixer (104). [15] The method according to claim 14, which further comprises: Digitizing an output signal y(t) of the RF receiver circuit; and Calculate at least part of the spectrum of the digitized signal (y[n]). [16] The method according to claim 15, which further comprises: Providing information concerning the linearity of the RF receiving circuit based on the spectrum of the digitized signal (y[n]). [17] The method according to claim 16, wherein the information relating to the linearity of the RF receiving circuit comprises information about spectral lines of the digitized signal (y[n]) that have no correspondence in the RF test signal (s RFTEST (t)) have. [18] An RF receiving device comprising the following: an antenna input for connecting an antenna (6); an RF signal source (101) designed to generate an RF oscillator signal (s LO (t)) to make available; a circuit for generating an RF test signal (s RFTEST (t)); a receiving mixer (104) having an RF input and an output, a coupler (110) connected to the antenna input, an output of the circuit for generating the RF test signal (s RFTEST (t)) and the RF input of the receiver mixer (104) and is configured to receive the RF test signal (s RFTEST (t)) to forward to the RF input of the receiving mixer (104); the circuit for generating the RF test signal (s RFTEST (t)) exhibits: an input circuit node coupled to the RF signal source (101) to generate the RF oscillator signal (s LO (t)) to receive; a first IQ modulator (111a) designed to generate a first RF signal ( SRF1 (t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a first signal (s1(t)); a second IQ modulator (111b) designed to generate a second RF signal (s RF2(t)) to generate by the RF oscillator signal (s LO (t)) is modulated with a second signal (s2(t)), where the first signal (s1(t)) and the second signal (s2(t)) are each complex-valued signals, each modulated by an in-phase signal component (s 1I (t), s 2I (t)) and a quadrature signal component (s 1Q (t), s 2Q (t)) are represented; and an RF combiner circuit (114) designed to generate an RF test signal (s RFTEST (t)) by combining the first RF signal ( SRF1 (t)) and the second RF signal (s RF2 (t)) to generate. [19] The RF receiving device according to claim 18, wherein the first signal (s1(t)) and the second signal (s2(t)) are single-tone signals that differ in their frequency and / or in their phase [20] A procedure that includes: Generating an RF test signal (s RFTEST(t)) by modulating several modulation signals that differ in pairs in their phase or in their frequency onto a high-frequency signal (s LO (t)) using the method according to any one of claims 12 to 17; and Injecting the RF test signal (s RFTEST (t)) into at least one RF circuit. [21] A circuit which has the following features: an input circuit node for receiving an RF oscillator signal (s LO (t)); a circuit (TSG) for generating a test signal (s RFTEST (t)) from the RF oscillator signal (s LO (t)) according to any one of claims 1 to 11; at least one receiving channel (RX01) with a receiver circuit and a coupler (110) designed to receive the RF test signal (s RFTEST (t)) to feed into the receiver circuit.

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