MARKET TRAINING MODULE

RF Control Products

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List of Content

Introduction RF Switches RF Attenuators

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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

15dB

24dB

9dB

1.9-

2.34

GH

z

1.25-1.8GHz

1.8-2.5GHz

870-1250MHz

2.5-3.4GHz

600-870MHz

450-600MHz

3.4-5GHz

10-450MHz

1768

2500

1250

3536

884

625a

5000

625b

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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

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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

RF Switches

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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

(Ex: SP8T)

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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

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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

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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

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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

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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)

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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

Note: PIN diode switches do not normally operate well at low frequency. They excel at high frequencies (60GHz and above).

Return Loss

Insertion Loss

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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 Power De-rating compared to therequired nominal powerthe switch can operate at

IP3Decrease at low frequencies

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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

SwitchingTime

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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)

RF1

RF2

RFC

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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)

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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)

RF Attenuators

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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

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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

G GA A

Input range Pin:From Pout-G+ATo Pout-G

Desired OutputRange: Pout

Signal Chain SNR Improved by G-NF-IL

Max PinMax Pin=Pin+A

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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

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RF Attenuators: State Error

Absolute Attenuation Error at each attenuation level, across the frequency and attenuation range

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RF Attenuators: Step Error

Relative Attenuation Error at each attenuation level, across the frequency and attenuation range

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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

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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

Reference Attenuator Circuit

Discrete Control CircuitPlease see Ref.4 from the Reference List

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Application Examples

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LO Generation

LPF

LPF

LPF

SP3T

Test In

LOFout

SP4T

• Remove Spurious and Harmonics• High Insertion loss (6dB+)• Could be Band Pass on selected

Paths

Brings LO level to Max allowedAnd desired by the follow-onCircuit (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

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RF Input Stage

DAT

G1

G2LNA

IL, RL impacts SNR Sets the signal levelIP3 impactsSystem linearity

Input ProtectionsRequired for high Pin

IN

Test in Or TX

OUT

SW1

SW2SW3 SW4 SW5

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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

Electrical Specification

Availability Loose parts abd evaluation boards available, pre-production Full production and general availability Q3’2015

Parameter Spec UnitsFrequency 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

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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 UnitsFrequency 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 SpeedtRise, tFall (10 / 90% RF)tON , tOFF (50% LE to 10 / 90% RF)

270/190 320/210

ns

ESD Rating Class2 (2kV) HBM

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Bibliography

1. Agilent Technologies, “Understanding RF/Microwave Solid State Switches and their Applications”, http://cp.literature.agilent.com/litweb/pdf/5989-7618EN.pdf

2. D. Fischer, R. Lourens, P. Bacon, “Overview of RF Switch Technology and Applications”, Microwave Journal, July 2014

3. National Instruments, “Complete Switching Tutorial”, http://www.ni.com/tutorial/3118/en/

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

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END