RF IV Waveform Measurement and Engineering

Transcription

1 RF IV Waveform Measurement and Engineering - Emerging Multi-Tone Systems - Centre for High Frequency Engineering School of Engineering Cardiff University Contact information Prof. Paul J Tasker tasker@cf.ac.uk website:

2 RF I-V Waveform Measurement & Engineering - Demand for Multi-Tone Excitation Synthesize real system stimulus Pulsed RF ~ - us Complex Modulation/Multi-Carrier Amplitude 3 Multi-Tone a(t) waveform Amplitude. Time... 5 Multi-Tone a(t) waveform Amplitude x -9 Time 345 x

3 RF I-V Waveform Measurement & Engineering - Demand for Multi-Tone Excitation CW (Single Tone) to Modulated (Multi-Tone) Measurement System Development RF Multi-Tone I-V Waveform Measurement Intelligent Sampling Inclusion of IF (Base-band signals) RF Multi-Tone IV Waveform Engineering IF (Base-band) active load-pull Application Memory Investigations: Base-band Electrical Memory CW (Single Tone) to Modulated (Multi-Tone) Measurement System Development RF Multi-Tone IV Waveform Engineering RF active load-pull (Digital ELP) 3

4 RF I-V Waveform Measurement & Engineering - Multi-Tone Measurement Requirements Need to extend sampling strategy to accommodate multi-tone excitation folded and interleaved sampling Need test-set architecture to account for all frequency components RF hardware between DUT and the sampling receivers ignores base-band components Microwave Source 4-channel Microwave Sampler Bias T Couplers Port Port Couplers Bias T Input DC Input DC 4

5 RF I-V Waveform Measurement & Engineering - Intelligent Sampling: Review CW Case CW Period Stimulus on a Specific Frequency Grid Sample over many RF cycles (M.P + C.Prime) M is the number of RF cycles contained within the sample period Engineer Sampling T s =M.T rf + C.Prime.T rf /P (P=sampled points, C=cycles), Multiple solutions f rf = f s.(m.p+c.prime)/p are sampled into Fourier location C If Prime (prime number) is greater than, time interleaving also occurs Independently Engineer the Fourier location of frequency components M=4 P=6 C= T s C.C 5

6 RF I-V Waveform Measurement & Engineering - Intelligent Sampling: Multi-Tone Case Multi-Tone Period Stimulus Sample over many modulated RF Cycles Independently engineer Fourier location of carrier (and harmonics) and modulation (and distortion) T s =N.T mod + T mod /P thus f mod = f s.(n.p+)/p (Fourier Location ) T s =M.T rf + C.T rf /P thus f rf = f s.(m.p+c)/p (Fourier Location C) M=5 N= P=8 C=5 With C=M/N M/N- M/N+ M=5 N= P=8 C=9 Spectral Compression With C M/N (=.Order+) C- C+ 6

7 RF I-V Waveform Measurement & Engineering - Multi-Tone versus CW fund Spectrally sparse Simple sampling (measurement) Only RF components Simple engineering DC harmonics ρ(t), Φ(t) Spectrally rich but grouped Envelope domain intelligent sampling RF and IF components measured engineered DC and IF fund harmonics 7

8 Non-Linear Vector Network Analyzer: - Basic Architecture with RF and IF Test-set Requires a very broadband four channel receiver Sweeper Utilizes integrated RF and IF directional couplers for detection/separation of waves Critical components Bias Tee/Diplexer Bias-Tee/Combiner IF Bis-Tee Bias T Couplers Couplers Port Port 4-channel Microwave Sampler Bias T Measures RF & IF a n (t) and b n (t) time varying Voltage Travelling Waves LF Bias T Input DC Sweeper Input DC LF Bias T 8

9 RF I-V Waveform Measurement & Engineering - Need for IF Measurements RF Components RF (Carrier + Harmonics) ω ω IF (Baseband) s IF Components s 5 4 DC/Δω 5 s 5 Waveform measurements necessitates all spectral components 9

10 RF I-V Waveform Measurement & Engineering - Classical IF Measurements and Data Presentation ω ω ω- ω ω- ω ω ω ω- ω ω ω ω- ω ω+ω Classical -tone often used Observation of IM magnitude and symmetry IM 3 L Limitation Little insight into sources of memory just the consequences Traditional Instrumentation - Spectrum Analysers, New Instrumentation - VSA, and recently PNA-X Pout [dbm] W 5 W IMD3L IMD3H IMD5L 5 Pin [dbm] Pref IMD5H 5

11 RF I-V Waveform Measurement & Engineering - Non-Classical IF Measurements and Data Presentation What is envelope domain analysis Powerful approach - intuitive Critical to to capture all significant spectral components DC, Baseband and RF spectra then used to rebuild the modulation envelope. Mag and Phase information key in this process. Freq Domain + Phase Dynamic transfer characteristics time domain envelope domain (without time)

12 RF I-V Waveform Measurement & Engineering - Non-Classical IF Measurements and Data Presentation Note-need phase infornation for all of these! dc Fo baseband Fo 3Fo +n Important - n All spectral information used in constructing the various envelope components +n Envelope Magnitude I C [ma] 4 3 DC f f f 3 Phaseº Envelope Phase I C[º]

13 3 RF I-V Waveform Measurement & Engineering - Investigation Linearity Issues (i.e. Memory) Surface effects Electrical effects evidence of memory Asymmetry Dynamic Looping Non-realiseable Digital Pre-distortion Thermal effects 3 Baseband In-band Out-of-band Combinations 3

14 Realization of IF (Base-band) Engineering - initial focus on bias circuit electrical memory issues Sweeper Δf 4Δf IF Source-pull Triplexer Bias T LF Bias T Couplers Port Port Couplers 4-channel Microwave Sampler (MTA Sampling Scope) Input DC Input DC Bias T LF Bias T Low frequencies Triplexer Passive solution physically very large Open-Loop Active Solution scaleable 6Δf 4Δf 6Δf Δf IF Load-pull 4

15 Realization of IF (Base-band) Engineering - initial focus on bias circuit electrical memory issues Here limited to Harmonics and 5 th Order Constant Impedance Environment Amplitude ω ω DC & IF RF (fundamental) W W Second harmonic IF IM5L IM3L IM3H IM5L IF High ω Investigate role of these signals on RF components - engineering the base-band impedance simplified two-tone spectrum up to fifth-order component polynomial transfer characteristic 5

16 IF Output Voltage Engineering (Envelope Tracking) - Effect on RF Carrier Output Power (HBT) IF Load-Pull Effect on Output Power and Efficiency Output Power [dbm] 6 7 Low ( ohm) Output Power [dbm] Variation around unity circle. 6 5 Carrier IC [ma] Low Short ( ohm) High Open (3 ohm) Frequency [GHz] V C [V] Efficiency [%] 3 High (3 ohm) Variation along real axis Output Power [mw] Ω Ω Ω 3Ω 6Ω 7Ω 8Ω Ω 5Ω 3Ω Output Power [mw] 3 Control of interaction of output dynamic waveforms with knee region explains carrier Power and efficiency sensitive to IF load impedance. 6

17 IF Output Voltage Engineering (Envelope Tracking) - Effect of Amplitude on Intermodulation Distortion (HBT) IF Load-Pull Effect on IM3 Distortion Carrier Variation Real Impedances along real axis IM3 Distortion [dbc] Ω Ω Ω 3Ω 6Ω 7Ω 8Ω Ω 5Ω 3Ω High (3 ohms) IM3 Low IM3 High Frequency [GHz] -5 IC [ma] 8 6 Low Short ( ohm) High Open (3 ohm) Low ( ohms) Output Power [dbm] Control of interaction of output dynamic waveforms with knee region explains intermodulation sensitive to IF load impedance. 3 V C [V]

18 IF Output Voltage Engineering (Envelope Tracking) - Effect of Amplitude on Intermodulation Distortion (HBT) a (Q Componenet) a (fundamental) 5-5 -x a (Q Componenet) Time Phase b (Q Componenet) b (fundamental) Time b (Q Componenet) Phase a (I Componenet) -x Time 5 -x -3 -x a (I Componenet) x b (I Componenet) Time 5 x b (I Componenet) -x -3 5 Time Time 5 8

19 IF Output Voltage Engineering (Envelope Tracking) - Effect of Phase on Intermodulation Distortion (HBT) IF Load-Pull Effect on IM3 Distortion Variation Reactive around Impedances unity circle Reactive 5 5 Output Power [dbm] Real IM3 Distortion [dbc] IC [ma] IC [ma] V C [V] 3 4 V C [V] Reactive Real Delta Current IM5 [ma] Delta Phase IM5 [ ] φ IM db Compression Output Power [dbm] IM3 Low 8 Mixing -y IM3 Product φ Mix x IM3 High Mixing y Carrier IM3 Low IM3 High Δ Frequency [GHz] IC [ma] IC [ma] Phase [ ] Phase [ ] Mixing of transfer and output non-linearities caused by interaction of dynamic output waveforms with knee region explains sensitivity to IF load impedance. 9

20 IF Output Voltage Engineering (Envelope Tracking) - Effect of Phase on Intermodulation Distortion (HBT) a (fundamental) 5-5 -x Phase b (fundamental) Phase a (Q Componenet) Time a (Q Componenet) b (Q Componenet) Time b (Q Componenet) a (I Componenet) -x -3 -x a (I Componenet) 5-5 -x -3 x Time 5 b (I Componenet) b (I Componenet) x Time 5 -x -3 5 Time Time 5

21 IF Input Voltage Engineering (Pre-distortion) - Effect on RF Carrier Output Power (HBT) IF Source-Pull Effect on Output Power and Efficiency 3 4 Output Power [dbm] Output Power [dbm] IC [ma] High (3 ohms) Carrier IC [ma] Low ( ohms) 5 open Variation around unity circle 3 4 Phase [ ] Frequency [GHz] 3 4 Phase [ ] Efficiency [%] 4 3 short open 4 6 short Ω Ω 5Ω 7Ω 8Ω Ω 5Ω 3Ω 6Ω Ω Open Variation along real axis I C [ma] Low ( ohms) High (3 ohms) 3 4 V C [V] Waveform shape explains carrier power and efficiency sensitive to IF source impedance

22 IF Input Voltage Engineering (Pre-distortion) - Effect on Intermodulation Distortion (HBT) IF Source-Pull Effect on IM3 Distortion IM3 Distortion [dbc] Variation Real Impedances along real axis!!! 3! 4! 5! 7! 8!! 5! 3! 6! Low ( ohms) High (3 ohms) Output Power [dbm] - Variation Reactive around Impedances unity circle Output Power [dbm] IC [ma] VBE [V] IB [ma] Low Short Circuit ( ohms) High 3! (3 ohms) 3 V C [V] v i (t) = A.v i (ω t) + B.v i (ω t) + C.v i (.Δωt) Phase [º] ! 5! 5! 3! 6! 35 7 i o (t) = a + a.v i (t) + a.v i (t) + a 3.v i (t) 3 Transfer function explains intermodulation sensitivity to IF source impedance

23 IF Input Voltage Engineering (Pre-distortion) - Optimization of Linearization Process (HBT) Q(t) Phase º Q(t) Phase º Input Voltage and Output Current Carrier Envelopes -x Phase º I(t) Phase º 3 3 Short Circuit Low ( ohms) Both Low and High) Input Voltage I(t) High 3! (3 ohms) Output Current Q(t) Q(t) Output Current [ma] Engineered Carrier Envelope Transfer Function! 5! 3! 6! Input Voltage [V].5.5 VB [V] Short Circuit IF VB [V] 3! IF Phase [ ] 6 Utilize IF source (input) impedance to engineering predistorted input signal I(t) - I(t) 3

24 Realization of IF (Base-band) Engineering - continue focus on bias circuit electrical memory issues Here limited to Harmonics and 5 th Order Amplitude Constant Impedance Environment ω ω DC & IF IF IF IM5L RF (fundamental) W W IM3L IM3H IM5L Second harmonic IF High W -W W - W 3 W - W W -W W W W -W 3 W - W W W + W W! Previous work investigated IM sensitivity to IF. simplified two-tone spectrum up to fifth-order component polynomial transfer characteristic But is some device, high power LDMOS base-band spectra is more complex 4

25 Linearity and Memory Investigations: - W Si LDMOS Waveform Engineering: Minimize Source of Electrical Memory.5 to 4.5 MHz AM Modulation (Two Tone:.f m ) Pout[dBm] IF(MHz to 9MHz) -.5 Tones - IM3L & IM3H Range Pin [dbm] Limitations of Passive Load-Pull) f m IM3L & IM3H.f m Range Tone-Spacing [MHz] Voltage [V] Pout [dbc] Range IMD3 Low IMD3 High Range Tone-Spacing [MHz] Range Observations Weak Memory Resulted Memory/Linearity sensitive to 4 times modulation BW Alghanim, EuMC 7 Range 5

26 IF Waveform Engineering - Optimum IF termination to simultaneously minimize IMD3 and IMD5 Measured IMD magnitude vs. phase of IF Measured IMD magnitude vs. phase of IF 4 3 W W 4 3 W W Pout [dbm] IMD3L IMD3H IMD5L IMD5H Pout [dbm] IMD3L IMD3H IMD5L IMD5H Phase of IF [degree] Phase of IF [degree].5. Improvement of IMD3 by -6 db and IMD5 by - db -.5 IF and IF termination

27 IF Waveform Engineering - Optimum IF termination to simultaneously minimize IMD3 and IMD5 Do these identified optimums change with tone-spacing?. Measured IMD magnitude vs. Pin 4.5. Pout [dbm] 3 - MHz IMD3L@MHz IMD3H@MHz IMD3L@MHz IMD3H@MHz IMD5L@MHz IMD5H@MHz IMD5L@MHz IMD5H@MHz IMD3 -.5 IF and IF termination - -3 IMD Pin [dbm] Indications are that the optimum IF impedances is independent of modulation frequency These impedances can be easily synthesised using an ET process 7

28 IF Waveform Engineering - Envelop Domain: Linearity Investigations Device: W LDMOS Carrier:. GHz Tone spacing: 8 khz, Bias A-B (%Idmax) Passive IF short S Radius=. j j5 IF j5 S Radius=. j j5 Voltage (V) Output IF Voltage Modulation of DC supply voltage Period dbm P in _avail = 4 dbm Frequency Grid point -j Upper Lower -j5 -j -j5 -j5 Drain Current (ma) Output Current Envelope Dynamic Power Sweep - b vs a Input Voltage Envelope Time (S)..x Gate Voltage (V) Pout (dbm) - 3 Pin (dbm) 4 8

29 IF Waveform Engineering - Demystifying Memory: Envelop Domain Simulations 7ps delay line used as DUT -tone excitation 8 MHz tone separation used imparts.8 degree phase shift onto the envelope Cause Dynamic range Envelope Dynamics.8 Dramatic effect 9

30 IF Waveform Engineering - Demystifying Memory: Active Device Measurements Device specifics W GAN Cree die. Fmax 4 GHz, gate width: x36um gate length.45um, Transit time.ps Gm=8uS. KHz (Quasi-Static) MHz 4 MHz Observations Dynamic trajectories are well aligned with quasi-static case. Again, under controlled conditions, becomes possible to expose delay. The delay here is bigger however (~45ps) than that observed for the 7ps delay line. This can be explained here by transit time and charge time for intrinsic parasitics 3

31 IF Waveform Engineering - Demystifying Memory: Active Device Measurements Observation Majority of Looping can be removed by applying an approximate -45 ps linear delay to the output envelope Observed delay can be explained (in this case) by intrinsic parasitic delay and transit time. τgm C gd C gs C ds Approximate intrinsic delay Cgs ~.7 pf ~ 35 ps Cgd ~.6 pf ~ 3 ps Cds ~.3 pf ~ 6 ps τgm ~ ps Total delay ~ 46 ps 3

32 IF Waveform Engineering - Envelop Domain: Linearity Investigations Input Voltage (V) Stimulate with Two-Tone Signal Analyze in Envelope Domain Device:.5 W GaN HFET Carrier:.8 GHz Tone spacing: 4 MHz, Passive IF short Investigate Dynamic Envelop Response Time DUT Output Current (ma) Transistor Memory RF Impedance variation Memory Input Voltage (V) Output Voltage (V) Input Voltage 8 3

33 RF I-V Waveform Measurement & Engineering - Demand for Multi-Tone Excitation CW (Single Tone) to Modulated (Multi-Tone) Measurement System Development RF Multi-Tone I-V Waveform Measurement Intelligent Sampling Inclusion of IF (Base-band signals) RF Multi-Tone IV Waveform Engineering IF (Base-band) active load-pull Application Memory Investigations: Base-band Electrical Memory CW (Single Tone) to Modulated (Multi-Tone) Measurement System Development RF Multi-Tone IV Waveform Engineering RF active load-pull (Digital ELP) 33

34 Realization of RF (Multi-Tone) Waveform Engineering - consider in-band and harmonic circuit electrical memory issues Sweeper Bias T Couplers Port Port Couplers Bias T 4-channel Microwave Sampler (MTA Sampling Scope) RF Load-pull Δf 4Δf IF Source-pull Triplexer LF Bias T Input DC Input DC LF Bias T Triplexer 6Δf 4Δf 6Δf Δf IF Load-pull 34

35 Realization of RF (Multi-Tone) Waveform Engineering - consider in-band and harmonic circuit electrical memory issues Sweeper Bias T Couplers Port Port Couplers Bias T Triplexer 3f f 4-channel Microwave Sampler (MTA Sampling Scope) Load pull Δf 4Δf IF Source-pull Triplexer LF Bias T Input DC Input DC LF Bias T Triplexer 6Δf 4Δf 6Δf Δf IF Load-pull 35

36 Realization of RF (Multi-Tone) Waveform Engineering - Envelope load-pull solution: Envelop Tracking Open loop at RF but a closed loop at envelope frequencies No loop oscillations as no direct RF feedback Reflection coefficient constant irrespective of the signal coming from DUT Impedances set by simple electronics controlled by the X & Y inputs Suitable for modulated signals DUT Demodulator X Y I Q Control Electronics I Q Modulator 36

37 Realization of RF (Multi-Tone) Waveform Engineering - Envelope load-pull solution: Envelop Tracking b(t) and a(t) waveforms Amplitude S Radius=. j5 S Radius=. j5 j Envelope Tracking Time j j Tone Modulated Signal => Confined to a few khz at present Constant Load -j -j5 -j -j5 -j5 37

38 Realization of RF (Multi-Tone) Waveform Engineering - Envelope load-pull solution: Instantaneous power sweeps Voltage (V) Voltage (V) s Time..5 s Time Pout (dbm) Pin (dbm) Gain S Radius=. j -j j5 j j5 -j -j5 S Radius=. j j5 -j5 Capture input (red) and output (blue) waveforms modulated with Hz Comparison between instantaneous and CW power sweep Impedance measured during instantaneous power sweep 38

39 Realization of RF (Multi-Tone) Waveform Engineering - Envelope load-pull solution: Envelop Tracking Open loop at RF but a closed loop at envelope frequencies No loop oscillations as no direct RF feedback Reflection coefficient constant irrespective of the signal coming from DUT Impedances set by simple electronics controlled by the X & Y inputs Need high speed control electronics for relevant bandwidth modulated signals: Digital Solution Required DUT Demodulator X Y I Q Control Electronics I Q Modulator 39

40 RF I-V Waveform Engineering - Next generation ELP Systems: Digital control using FPGA DSP development board Stratix II edition FPGA is Altera Stratix II clocked at MHz Two-channel, bit, 5-MSPS A/D converter Two-channel, 4 bit, 65-MSPS D/A converter The multi-tone measurement system is clocked by MHz derived clocked from the FPGA master clock The control algorithm is implemented in time domain Frequency domain control will offer more functionality such as individual tone control enable emulation of real world impedance matching network 4 4

41 ..5 M M 5-6 RF I-V Waveform Engineering - Next generation ELP Systems: Time Delay problem a b 5. L x - 5 L K K s The control unit can support wideband stimulus albeit delay Phase variation over length of cable and components (group delay or envelope delay) Must be compensated for accurate load impedance matching The repetitive nature of the measurement stimulus made delay compensation possible in the next repetition or N repetition later 4

42 RF I-V Waveform Engineering - Next generation ELP Systems: Delay compensation determination Configurable FIFO RAM based unit delay Unit delay is ns ( MHz clock) Delay is compensated after 76 delay elements Latest development of delay compensation is not limited to unit delay Linear group delay can be observed from the graph Delta Phase (degree) Delta Phase (M-M) Delta Phase (L-L) Delta Phase (K-K) Delay Element

43 RF I-V Waveform Engineering - Next generation ELP Systems: Digital control using FPGA using delay a b 5-6 x -5 - s 3 4 Delay compensation results Smith chart showing compensated delay (zoom) 43

44 RF I-V Waveform Engineering - Next generation ELP Systems: Two-Tone Signal with MHz separation. Low High.5. IM3_low F IM5_low Tones -.5 IM3_high F IM5_high -. Constant Impedance over MHz bandwidth IM3 Output power (dbm) Input power (dbm) F F IM3L IM3H IM5L IM5H IM5 44