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RF Control Products Training Module


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An Introduction to ADI’s RF Switches and RF Attenuators including their key characteristics and how and where they should be used in the RF signal chain.

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RF Control Products Training Module

  1. 1. MARKET TRAINING MODULE RF Control Products
  2. 2. List of Content ► Introduction ► RF Switches ► RF Attenuators 2
  3. 3. Introduction ► Control Products are defined as impacting the signal chain performance  By configuring the Chain  By adjusting the signal level  NOT amplifying or converting the signal (i.e. ideally linear and passive)  Operating Frequency above 1GHz to close to 100GHz ► RF Switches (SPST, SPDT, SP3T, SP4T, etc.) ► RF Attenuators (Digital, i.e. DAT, Analog) ► TX/RX Switches 3 15dB 24dB9dB 1.9- 2.34GHz 1.25- 1.8GHz 1.8- 2.5GHz 870- 1250MHz 2.5- 3.4GHz 600- 870MHz 450- 600MHz 3.4- 5GHz 10- 450MHz 176 8 250 0 125 0 353 6 88 4 625a 500 0 625 b
  4. 4. Application and Marketing Considerations ►ALL RF Systems/PCB include RF Switches and often RF Attenuators  Some systems (PCB) have 30 to 50 RF switches and few attenuators  Examples:  Inserting a calibration signal in the Signal Chain  Bypassing fixed-gain amplifiers  Routing a signal to different (frequencies) downconversion chains  Routing an LO signal thru alternative frequency selective gains, before the mixer  Optimizing the RF signal level for best noise performance, after a fixed gain stage (LNA) or between fixed gain stages 4
  5. 5. RF Control Product: Common Basic Knowledge ► RF Devices, packaged for PCB usage ► RF “Connectorized” Components, to be used as stand alone ► Passive, i.e. always have a transfer attenuation ► RF Switches key function is to route Signals to different Signal Chains ► RF Attenuators key function is to maintain the RF Signal Levels to the planned ranges for best system performance ► Controlled Signals are  Information signal (receive, transmit)  Clocks, Local Oscillators 5
  6. 6. RF Switches
  7. 7. RF Switches: Naming ► Single Pole Single Throw (SPST) ► Single Pole Dual Throw (SPDT) ► Single Pole “X” Throw (SPXT) ► Notes  Double Pole (e.g. in a DPDT) normally called “Differential”  RF circuits are normally single ended 7 (Ex: SP8T)
  8. 8. RF Switches: Grouping ► Electromechanical (EM) switches  Lower Reliability and Life Time  High Electrical Performance (after switching transitions) ► Solid State (SS) switches  High Reliability and Life Time  Good Electrical and Switching Performances ► Micro-Electro Mechanical switches (MEMS)  Promising both EM and SS like characteristics  Lower Operating frequencies than SS  Part of ADI IP 8
  9. 9. RF Solid State Switches: technological options ► FET-based switches  GaAs – Fast, High Frequency capability (100Hz), less robust (ESD)  Silicon – getting faster, good settling time, med Frequency (20-40GHz), robust ► Pin Diode switches  High frequency (100GHz), robust, difficult to drive/control ► Hybrid (FET and Pin Diode)  Combination of both the above  May not allow a monolithic solution 9
  10. 10. RF Switches: System Level Characteristics 1 of 2 ► Architecture  Absorptive – includes a matched impedance (Typically 50 Ohms) on the input when the switch is open, so the circuit driving the input will see a matched impedance at all times (across the operating frequency range)  Reflective – has no matched impedance when open, so the driving circuit needs to be able to handle the reflected waves and power ► Control Signals (FET)  Direct Control and low power control signals  May suffer from RC delay  May require negative voltage control signals to operate the switch ► Power Supplies  Need most often to have both polarities supply voltage  The negative supply voltage can be internally generate, at the expense of a higher system noise, from the integrated charge pump 10
  11. 11. RF Switches: System Level Characteristics 2 of 2 ► DC coupling  ALL Traditional RF switches do not like DC signal through them  DC decoupling caps are needed, unless a 0Vdc can be guaranteed  Decoupling Caps will impact the low frequency performance  New Technology in development with DC handling capability ► Power consumption  Low static power consumption (100-300uA) ► Reliability (SS)  Highest among available technologies  GaAs switches have low ESD threshold, requiring specific care 11
  12. 12. RF Switches: Electrical Characteristics ► Frequency Range (from 1-2GHz to 80GHz+) ► Insertion Loss (normally lower than 0.5dB, or max 1dB) ► Return Loss (normally higher than 10-15dB) ► Power Handling (the higher the better, now around 30dBm, moving to 40dBm+) ► Isolation (normally in the 25-50dB, frequency dependent) ► Distortion/Linearity (normally high, above 50dBm) ► Switching Speed (from 10ns to 1us depending on used processed, GaAs is faster, Si is slower) ► Settling Time (from 100ns to 5us depending on the fabrication process used, Si is slower, but has a shorter settling time) ► Noise (Leakage, switching) 12
  13. 13. Operating Frequency Range – Insertion Loss (IL), Return Loss (RL) ► Frequency Range is commonly the FIRST selection criteria for switches ► Insertion Loss is mostly impacted by  The switch’s direct intrinsic resistance  Reflected Loss as of the switch resistance  Leakage paths, which reduce the useful signal power to the load  IL must be compensated for by other circuits or taken into account when performing level planning (as it impacts noise performance) ► Frequency dependent IL  Low Frequency IL is affected by  Any decoupling Cap at the In/Out leads  Power handling (see later) capability  High Frequency IL is affected by  Intrinsic parasitic capacitances  In band IL variation is affected by  Return Loss, caused by impedance mismatching ► Return Loss (RL)  Indicates the amount of power not transferred over the switch (but reflected back)  Depends on the impedance matching (50OHM) of the switch with the externally connected devices 13 Return Loss Insertion Loss
  14. 14. Signal Power Handling and Distortion ► Switch capability to handle high power signals  Allows to deploy switches closer to the system RF connectors  Decreases at lower frequencies, as limited by process technology and switch architecture  Defined while the switch is static or switching (Hot switching power)  Described by P1dB (or PSAT) ► Distortion  Measured by IP3  Related with Power handling  Approaching P1dB non linearity increases (IP3 decreases)  Normally the Switch is not the critical Signal Chain block on distortion 14 Power De-rating compared to the required nominal power the switch can operate at IP3 Decrease at low frequencies
  15. 15. Switching Speed & Settling Time ► Switching Speed (or Time) – Time from 50% of switching control Input to 90% of the RF signal out. ► Settling Time – Referred to the time the RF signal has set to 0.05dB or 0.01dB from its final time  Settling Time is a particular challenge for GaAs switches 15 Switching Time
  16. 16. Isolation ► Signal going through the switch when it is OFF  From the common I/O to any other port  Between two different ports ► Normally NOT the coupled noise from the control ports (see later) ► FET switches have very high low frequency isolation  Drain-Source Cap is limiting high frequency isolation  This can be improved by shunting the input port to ground when the switch is open (implemented inside the switch itself) ► Pin Diode Switches have good high-frequency isolation (and poor isolation at low frequencies) 16 RF1 RF2 RFC
  17. 17. Other Noise and Sources of Interference ► Video leakage or feedthrough  Describes the noise from the control ports to the RF ports  Normally measured when no RF is present (reported in mV)  Lower in FET switches  Critical is some applications (for example when a high gain AGC amplifier follows the switch) ► Power Supply Noise  From external supplies – to be managed by proper filtering  From internal bias voltages (normally negative) generated by an integrated charge pump  Typically avoided by high end applications (T&M) 17
  18. 18. RF Switches - Application Topics ► RF Ports Coupling - Traditional RF switches are not taking any DC signal  Requiring DC decoupling at the ports.  Impacting the IL at low frequencies. Proper selections of the Caps would depended on the desired low frequency performances.  Decoupling Caps can be avoided if the operating signals have no DC component (this is mentioned often in datasheets as “not needing any decoupling Cap”!!!) ► Power Supplies  Switches can operate from single supply or from dual supplies  A competitor has integrated the Vneg supply, with the related system noise drawback ► Power Handling  A critical system parameter, in many application, as the switch might need to be protected, especially at low frequencies (below 10-100MHz)  Improved handling is achieve with Si based switches ► Control Signals – voltage ranges, drive  Control voltage polarity depends on the switch supplies, and can be also negative voltages  Latest switches operate with positive voltages (compatible with standard logic levels), and have bipolar supplies  Solid state switches are easy to drive (unlike some PIN Diode based switches) 18
  19. 19. RF Attenuators
  20. 20. RF Attenuator Typicales ► Fixed Attenuators (“Pads”) ► Digitally-Controlled Attenuators (DAT)  Serial or parallel Control  Series of switched-in/out fixed attenuators  Resolution from 1bit to 7bit ► Analog (Voltage) Controlled Attenuators (VVA)  More complex control architecture  Preferred when in AGC loops or for high signal level accuracy 20
  21. 21. RF Attenuators: WHY? ► Key justification for Attenuators  Achieve a more optimized signal level plan (for noise and distortion)  RF amplifiers have commonly fixed gain  RF amplifiers may not like high power input signals 21 G G A A Input range Pin: From Pout-G+A To Pout-G Desired Output Range: Pout Signal Chain SNR Improved by G-NF-IL Max PinMax Pin=Pin+A
  22. 22. RF Attenuators: Main and Common to the RF switches Electrical Characteristics ► Frequency Range: Operating Frequency Range ► Attenuation Range: discrete or continuous ► Attenuation Resolution (DAT): minimum nominal attenuation step, in dB. Related to the bit count and Attenuation Range  E.G., 32dB range, 6 control bits (64 levels) gives 0.5dB resolution, to a max attenuation of 31.5dB (0dB attenuation included) ► Attenuation Accuracy: nominal accuracy. Normally reported across frequency and attenuation range ► Insertion Loss: Attenuation across the device, when 0dB is selected (ideally no attenuation applied) ► Return Loss: reflected Power at the Input/Output ports, related to the device impedance matching ► Power Handling (P1dB, P0.1dB): maximum input signal power, the device can handle and keep operating linearly. Normally reported across the frequency range. ► Distortion/Linearity (IIP3): see RF Switch description, normally reported across the attenuation range ► Switching Speed: see RF Switch description ► Settling Time: see RF Switch description, normally reported across the attenuation range ► Overshoot Free DAT: the Attenuator output presents no overshooting voltage, when switching between any attenuation steps, as a consequence of how the internal attenuation switches are operated ► Power Supplies, Control Voltages: see RF Switch description 22
  23. 23. RF Attenuators: State Error Absolute Attenuation Error at each attenuation level, across the frequency and attenuation range 23
  24. 24. RF Attenuators: Step Error Relative Attenuation Error at each attenuation level, across the frequency and attenuation range 24
  25. 25. RF Attenuators: Phase Variation Relative Phase variation from the output to the input signal, as it goes through the different internal attenuation steps  Normally reported as max value, across the frequency and attenuation range  Also reported as graph 25
  26. 26. Analog Attenuators (VVA) • Similar Function as with VGA, but implemented with an Attenuator (as “programmable wideband RF Amplifiers are rare”). • Key technical challenges • Maintain Insertion Loss and Return Loss performances in the attenuation range, across frequency range • Linear relationship with the control voltages • Simplify control circuitry 26 Reference Attenuator Circuit Discrete Control CircuitPlease see Ref.4 from the Reference List
  27. 27. Application Examples 27
  28. 28. 28 LO Generation LPF LPF LPF SP3T Test In LO Fout SP4T • Remove Spurious and Harmonics • High Insertion loss (6dB+) • Could be Band Pass on selected Paths Brings LO level to Max allowed And desired by the follow-on Circuit (eg mixer) • Amplifies Fout • Isolates Fout from downchain • May be omitted, with certain Fout Critical Parameters • Low insertion Loss • High Return Loss • High Linearity End Application Dependent • Low video Leakage • Fast Switching/Settling • Power Handling Non Critical Parameters • Isolation
  29. 29. 29 RF Input Stage DAT G1 G2 LNA IL, RL impacts SNR Sets the signal level IP3 impacts System linearity Input Protections Required for high Pin IN Test in Or TX OUT SW1 SW2 SW3 SW4 SW5
  30. 30. HMC1118LP3DE 9KHz-13GHz SPDT (New Product) High Isolation Silicon Switch ► Features  Non-Reflective 50 Ω Topology  Wideband solution with excellent Isolation 56dB @8GHz  Fast 0.1dB Settling Time of 7.5us(Critical for T&M apps)  Optimized for Low Frequency operation down to 9KHz  No DC Blocking Cap is required on RF pins.  Flat Insertion Loss across Frequency : Less than 0.2dB variation up to 9GHz.  High Input IP3: +62 dBm @ 3.0 GHz  Optimum for High power apps: High P1dB: >+37dBm  High Power Handling: +36dBm through, +27dBm terminated/hot-switching  Positive Control, 0/+3.3 V  Excellent ESD Rating: 2 kV HBM  RoHS Compliant 3x3 mm 16 Lead QFN Package ► Device Pin-out 30 ► Electrical Specification ► Availability  Loose parts abd evaluation boards available, pre-production  Full production and general availability Q3’2015 Parameter Spec Units Frequency Range 9 kHz - 13.0 GHz Insertion Loss @ 0.1 GHz 0.45 dB Insertion Loss @ 8.0 GHz 0.60 dB Insertion Loss @ 10.0 GHz 0.90 dB Isolation @ 0.1 GHz 81 dB Isolation @ 8.0 GHz 56 dB Isolation @ 10.0 GHz 35 dB Input P1dB @ 3.0 GHz +37 dBm Input IP3 @ 3.0 GHz 62 dBm Switching Speed 2.7 μs Settling Time 0.1dB 7.5 μs Settling Time 0.01dB 12 μs Bias Voltage VDD +3.3 V Bias Voltage VSS -2.5 V ESD Rating Class 2 (2kV) HBM
  31. 31. 31 HMC1119LP4E 0.1-6GHz 0.25dB LSB 7-bit (New Product) Overshoot Free Digital Attenuator ► Features  7-bit 0.25 dB LSB Steps to 31.75 dB  High Input IP3: +55 dBm  Overshoot Free Operation  Low insertion loss of 1.2dB @2GHz  Typicalical step error of ±0.2dB  TTL/CMOS compatible contol interface  High ESD robustnest of 2KV HBM  Single +3.3V to +5V supply  RoHs 4x4mm SMT compliant package ► Device Pin-Out ► Availability  Loose parts and evaluation boards available. X-Grade production.  Full production and general availability Q3’15 ► Electrical Specification Parameter Spec Units Frequency Range 0.1 – 6.0 GHz Atenuation Resolution (LSB) 0.25 dB Attenuation Accuracy : ± 0.25 (3%) dB Insertion Loss @ 0.1 GHz 1 dB Insertion Loss @ 2 GHz 1.2 dB Insertion Loss @ 4 GHz 1.7 dB Phase var. over attenuation range @ 2 GHz 16 deg P0.1dB @ 0.1 GHz 32 dBm P0.1dB @ 4 GHz 32 dBm Input IP3 @ 0.1 GHz 55 dBm Input IP3 @ 4 GHz 52 dBm Input Return Loss < 6 GHz 17 dB Output Return Loss < 6GHz 18 dB Supply Voltage +3.3 to +5 V Control Interface Ser./ Par - Control Voltage 0/3.3 or 0/5 V Switching Speed tRise, tFall (10 / 90% RF) tON , tOFF (50% LE to 10 / 90% RF) 270/190 320/210 ns ESD Rating Class2 (2kV) HBM
  32. 32. Bibliography 1. Agilent Technologies, “Understanding RF/Microwave Solid State Switches and their Applications”, 2. D. Fischer, R. Lourens, P. Bacon, “Overview of RF Switch Technology and Applications”, Microwave Journal, July 2014 3. National Instruments, “Complete Switching Tutorial”, 4. “Designing with the HMC346MS8G Voltage Variable Attenuator”, Hittite Microwave, Product Note 5. Gary Breed, “A Review of RF/Microwave Switching technologies”, High Frequency Electronics, May 2010, pag.70 32
  33. 33. END 33