Method of measuring the AM/PM conversion of a device under test

Abstract

A method of measuring the AM/PM conversion of a device under test having a local oscillator is described. A device under test with an embedded local oscillator is provided. A signal source is connected to an input of the device under test. A receiver is connected to an output of the device under test. An input signal is provided by the signal source. The input signal has an initial power level. The input signal is input to the device under test. The power level of the input signal is changed. An output signal of the device under test is measured at different power levels of the input signal.

Claims

1. A method of measuring the AM/PM conversion of a device under test having a local oscillator, with the following steps: providing a device under test with an embedded local oscillator, connecting a signal source to an input of said device under test, connecting a receiver to an output of said device under test, providing an input signal by said signal source, said input signal having an initial power level, said input signal being input to said device under test, changing the power level of said input signal, and measuring an output signal of said device under test at different power levels of said input signal, wherein the power level of a certain measurement is lower than the power level of a previous measurement and lower than the power level of a subsequent measurement.

2. The method according to claim 1, wherein said receiver is centered on an anticipated frequency span of the output signal.

3. The method according to claim 1, wherein said receiver is centered on an anticipated frequency span of the output signal for each power level used for a measurement.

4. The method according to claim 1, wherein the power level of said previous measurement is different to the power level of said subsequent measurement.

5. The method according to claim 1, wherein the power level of said previous measurement is lower than the power level of said subsequent measurement.

6. The method according to claim 1, wherein the power level is changed between said initial power level and a maximum power level.

7. The method according to claim 1, wherein a power sweep is used for changing the power level.

8. The method according to claim 1, wherein a local oscillator signal is constant while the power level is changed.

9. The method according to claim 1, wherein said input signal with the initial power level corresponds to a reference signal.

10. The method according to claim 1, wherein the power level of said input signal is varied so as to provide at least one signal pulse.

11. The method according to claim 1, wherein the power level of said input signal is varied so as to provide several signal pulses.

12. The method according to claim 11, wherein a signal pulse has a power level being higher than the power level of a previous signal pulse.

13. The method according to claim 10, wherein the power level of said input signal is lowered to the initial power level after the at least one signal pulse.

14. The method according to claim 10, wherein phase values measured prior and after the at least one signal pulse are averaged to obtain an average phase value at the initial power level.

15. The method according to claim 10, wherein a phase value is measured at the at least one signal pulse.

16. The method according to claim 14, wherein the average phase value is compared with the phase value measured at the at least one signal pulse.

17. The method according to claim 14, wherein the average phase value at the initial power level corresponds to a reference phase that is updated regularly.

18. The method according to claim 1, wherein a ramp for the power level of said input signal is started, the power level being increased by a small increment of the total ramp and a measurement being conducted, the power level being reduced by a portion of said small increment to adapt the power level and a measurement being conducted.

19. The method according to claim 18, wherein the small increment is a tenth of the total ramp or less.

20. The method according to claim 1, wherein a ramp for the power level of said input signal is started that has a substantially triangular shape.

Description

DESCRIPTION OF THE DRAWINGS

(1) The foregoing aspects and many of the attendant advantages of the claimed subject matter will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:

(2) FIG. 1 schematically shows a system that is used for performing a representative embodiment of a method of measuring the AM/PM conversion according to the present disclosure;

(3) FIG. 2 schematically shows a flow-chart illustrating an example of a method of measuring the AM/PM conversion according to the present disclosure;

(4) FIG. 3 shows a diagram illustrating the changing power level according to an aspect of the present disclosure; and

(5) FIG. 4 shows another diagram illustrating the changing power level according to another aspect of the present disclosure.

DETAILED DESCRIPTION

(6) The detailed description set forth below in connection with the appended drawings, where like numerals reference like elements, is intended as a description of various embodiments of the disclosed subject matter and is not intended to represent the only embodiments. Each embodiment described in this disclosure is provided merely as an example or illustration and should not be construed as preferred or advantageous over other embodiments. The illustrative examples provided herein are not intended to be exhaustive or to limit the claimed subject matter to the precise forms disclosed.

(7) In FIG. 1, a system 10 is shown that comprises a device under test 12 as well as a vector network analyzer 14 having a signal source 15. Therefore, the vector network analyzer 14 corresponds to the signal source 15. As shown in FIG. 1, the device under test 12 comprises an input 16 to which the vector network analyzer 14 is connected. The input 16 is established at an intermediate frequency (IF) side 18 of the device under test 12.

(8) The device under test 12 also has an output 20 to which a receiver 22 is connected that is integrated in the vector network analyzer 14. The output 20 is established at a radio frequency (RF) side 24 of the device under test 12. Accordingly, the vector network analyzer 14 comprises the signal source 15 as well as the receiver 22.

(9) Thus, the vector network analyzer 14, for example the signal source 15, generates an input signal that is input to the intermediate frequency side 18 of the device under test 12. The device under test 12 processes the input signal internally wherein an output signal is provided at the radio frequency side 24 that is forwarded to the receiver 22, namely the vector network analyzer 14. Thus, the vector network analyzer 14 is configured to analyze the output signal of the device under test 12 appropriately. The internal processing of the input signal is done by an embedded local oscillator 26 that uses a local oscillator signal.

(10) With reference to FIG. 2, a representative embodiment of a method of measuring the AM/PM conversion of the device under test 12 will be described hereinafter.

(11) In a first step S1, the device under test 12 with the embedded local oscillator 26 is provided. In a second step S2, the vector network analyzer 14, for example the signal source 15, is connected to the input 16 of the device under test 12. In a third step S3, the receiver 22, namely the vector network analyzer 14 itself, is connected to the output 20 of the device under test 12.

(12) In a fourth step S4, an input signal is provided by the vector network analyzer 14, for example the signal source 15, wherein the input signal has an initial power level at least at the beginning. The input signal provided by the vector network analyzer 14 or the signal source 15 is input to the device under test 12 via its input 16 so that the input signal is internally forwarded to the local oscillator 26 of the device under test 12 for internal processing. The device under test 12 then generates an output signal based on the input signal which is forwarded to the receiver 22, namely the vector network analyzer 14, via the output 20 of the device under test 12.

(13) In a fifth step S5, the receiver 22 or the vector network analyzer 14 measures, analyzes, etc., the output signal provided by the device under test 12 so as to measure the phase.

(14) In a sixth step S6, the power level of the input signal is changed significantly so that the output signal of the device under test 12 is also changed. In a seventh step S7, the receiver 22 or the vector network analyzer 14 is centered on an anticipated frequency span of the output signal of the device under test 12.

(15) In an eighth step S8, the output signal of the device under test 12 is measured at a different power level of the input signal with regard to the power level of the input signal provided at the fifth step S5.

(16) In some embodiments, the above mentioned steps, namely steps S5 to S8, are repeated iteratively so that the input signal is changed with regard to its power level several times wherein the output signal of the device under test 12 is measured for the different power levels of the input signal. Further, the receiver 22 or the vector network analyzer 14, is centered regularly. Thus, the receiver 22 or the network analyzer 14 is centered for each power level used for a measurement. This ensures that the receiver window is quite small so as to ensure a high accuracy for the respective measurement.

(17) It is further at least assumed that the local oscillator signal forwarded to the local oscillator 26 is constant while the power level is changed.

(18) In some embodiments, the power levels are changed such that the power level of a certain measurement is lower than the power level of a previous measurement and lower than the power level of a subsequent measurement. This becomes obvious in FIGS. 3 and 4 showing exemplary power level changes during the respective AM/PM conversion measurements.

(19) In FIG. 3, a representative power level change is shown that can be used during the measurement of the AM/PM conversion of the device under test 12. As shown in FIG. 3, the input signal starts at an initial power level that is indicated as reference power P.sub.ref. In some embodiments, the input signal with the reference power P.sub.ref corresponds to a reference signal.

(20) Then, the power level of the input signal is increased to a first power level indicated as minimum power level P.sub.min, wherein the power level is decreased afterwards to the initial power level again, namely the reference power P.sub.ref. Next, the power level of the input signal is increased again to a second power level that is higher than the first power level, namely the minimum power level P.sub.min, wherein the power level is decreased back to the initial power level or rather the reference power level P.sub.ref.

(21) The signals with the first power level as well as the second power level correspond to signal pulses which becomes obvious from FIG. 3. The signal pulses have different power levels.

(22) In some embodiments, several signal pulses are provided each having power levels higher than the initial power level or rather the reference power level P.sub.ref. As shown in FIG. 3, the power level of each signal pulse is higher than the power level of the previous signal pulse so that a power sweep, for example an increasing power sweep, for the signal pulses is provided. The power sweep starts at the minimum power level P.sup.min. wherein the power level is increases for each signal pulse until a maximum power level P.sup.max, is reached. Thus, a power sweep or rather a ramp is used for the signal pulses since the respective power levels of the signal pulses increase continuously.

(23) As indicated in FIG. 3, the power level is returned back to the initial power level or rather the reference power level P.sub.ref after each signal pulse.

(24) Moreover, the phase of the output signal is measured by the receiver 20 or the vector network analyzer 14 for each different power level, namely every time the power level is decreased to the initial power level or rather the reference power level P.sub.ref as well as the different high power levels at the respective signal pulses. This is indicated by the respective phase values .sub.x shown in FIG. 3.

(25) Further, an average phase value is determined by averaging the phase values measured prior and after each signal pulse so as to obtain a reference phase used for comparison with the phase value measured at the assigned signal pulse.

(26) In general, the average phase value can be indicated as follows:

(27) ${\stackrel{\_}{}}_{x,x+2}=\frac{{}_x+{}_{x+2}}{2},$

(28) wherein x is odd-numbered, namely 1, 3, 5, 7 and so on. For instance, the first average phase value can be determined by:

(29) ${\stackrel{\_}{}}_{1,3}=\frac{{}_1+{}_3}{2}$

(30) As mentioned above, the average phase value determined is compared with the signal pulse assigned thereto, namely the signal pulse that is located between the phase values measured prior and after the respective signal pulse at the initial power level or the reference power level P.sub.ref. Thus, the phase value of the signal pulse can be indicated generally as .sub.y,

(31) wherein y is even-numbered, namely 2, 4, 6, 8 and so on.

(32) In some embodiments, the phase of the output signal is measured at the beginning, namely at the initial power level or the reference power level P.sub.ref, so that the phase value .sub.1 is obtained. Then, the phase of the output signal is measured at the first signal pulse, so that the phase value .sub.2 is obtained.

(33) Moreover, the phase of the output signal is measured when the power level is decreased to the initial power level or rather the reference power level P.sub.ref, so that the phase value .sub.3 is obtained.

(34) The phases or rather phase values measured prior and after the respective signal pulses having the first power level are averaged so that a reference phase is obtained for the first signal pulse having the first power level. This reference phase obtained is compared with the phase measured at the first signal pulse.

(35) The reference phase is updated regularly for each signal pulse by averaging the phase values measured prior and after the respective signal pulse. The advantage of this approach is that a reference phase is determined for each signal pulse so that frequency drifts of the local oscillator 26 can be taken into account since the reference phase is updated several times during the measurements, namely for each signal pulse.

(36) In general, the measurement of the phase that takes place after the first signal pulse may relate to a certain measurement which power level is lower than the power level of the previous measurement, namely the previous signal pulse, and lower than the power level of the subsequent measurement, namely the subsequent signal pulse. In some embodiments, the power levels of the previous signal pulse as well as the subsequent signal pulse are higher than the power level of the certain measurement.

(37) In FIG. 4, another approach for changing the power level of the input signal significantly over time is shown. In this approach, the power level of the input signal is ramped wherein the power level starts at the initial power level or rather the reference power level P.sub.ref. The power level is increased to a maximum power level P.sub.max. Then, the power level is reduced or rather decreased from the maximum power level P.sub.max back to the initial power level or rather the reference power level P.sub.ref as shown in FIG. 4.

(38) Accordingly, this approach corresponds to a triangular approach since the ramping of the power level corresponds to a triangular ramp.

(39) However, the ramping of the power level is split since the power level is increased by a small increment 28 of the total ramp to provide a power level at which a measurement is done. Then, the power level is decreased by a portion 30 of the small increment 28 so that another power level is provided at which a measurement is done.

(40) The increasing and decreasing take place several times or iteratively until the maximum power level P.sub.max is reached. From the maximum power level P.sub.max, the power level for the different measurements is decreased in a mirrored manner since the power level is decreased by a small increment 32 of the total ramp to provide a power level at which a measurement is done wherein the power level is increased by a portion 34 of the small increment 32 so that another power level is provided at which a measurement is done.

(41) The decreasing and increasing take place several times or iteratively until the initial power level or rather the reference power level P.sub.ref is reached.

(42) The small increments 28, 32 may have the same amount. In addition, the portions 30, 34 may have the same amount.

(43) Therefore, hysteresis effects that may occur in the device under test can be monitored appropriately.

(44) In some embodiments, the small increment 28, 32 used for increasing or decreasing the power level may correspond to a tenth of the total ramp or less that is used for changing the power level.

(45) In general, the AM/PM conversion of the device under test 12 having the embedded local oscillator 26 can be measured directly and effectively wherein the accuracy desired is obtained.

(46) In addition, hysteresis effects as well as local oscillator drifts, namely frequency drifts of the local oscillator 26, can be taken into account in an appropriate manner so that an improved measurement of the AM/PM conversion of the device under test 12 is done.

(47) The principles, representative embodiments, and modes of operation of the present disclosure have been described in the foregoing description. However, aspects of the present disclosure which are intended to be protected are not to be construed as limited to the particular embodiments disclosed. Further, the embodiments described herein are to be regarded as illustrative rather than restrictive. It will be appreciated that variations and changes may be made by others, and equivalents employed, without departing from the spirit of the present disclosure. Accordingly, it is expressly intended that all such variations, changes, and equivalents fall within the spirit and scope of the present disclosure, as claimed.