ELEN 701 RF & Microwave Systems Engineering

Lecture 8November 8, 2006

Dr. Michael ThorburnSanta Clara University

System Noise Figure

GAIN = G

Signal S1

Noise N1

Self Noise No

Signal G x S1Noise G x (N1+No)

( ) 1

0

1

01

01

1

1

1

1NN

NNN

NNggS

NS

F +=+

=

+

=

Noise Figure of a Passive Device

1)(

)(

1

00

02

01

12

102

1

0

==

==

=+=

+=

gFFBkTgBkT

BkTNBkTN

FgNNNNgN

NNF

Suppose Passive Device is at ambienttemperature and that input noise is also at ambient temperature

GAIN = GSignal S1Noise N1

Self Noise No

Signal G x S1Noise G x (N1+No)

Transmitter System Analysis and Design

• Adjacent and Alternate Channel Power– Low-Pass Equivalent Behavioral Model Approach– Multitone Techniques– ACPR of Cascaded Stages in Transmitter Chain

• Noise-Emission Calculation– Formula– Some Important Notes

• Output Noise of an Attenuator• Output Noise Floor of Device or Transmitter

• Some Important Considerations in System Design– Transmitter Chain Gain Distribution and Performance

Transmitter System Analysis and DesignAdjacent and Alternate Channel Power

Low-Pass Equivalent Behavior Model Approach• Adjacent and Alternate Channel Power

– Adjacent channel power ratio (ACPR) is ratio of power in adjacent channel to the power in the desired channel

– The alternate channel power ratio is the ratio of power in a specified alternate channel to the power in the desired channel

– Sketch picture on board

• Low-Pass Equivalent Behavioral Model Approach– The adjacent/alternate channel powers mainly result from spectral

regrowth caused by the nonlinearity of the transmitter chain, which mostly comes from the power amplifier and the driver amplifier

– The ACPR of a digitally modulated transmission signal cannot be accurately determined from intermodulation distortion of discrete tones

• A nonlinear model, developed from AM-Am and AM-PM measurement or simulation is used

Transmitter System Analysis and DesignAdjacent and Alternate Channel Power

Low-Pass Equivalent Behavior Model Approach

• Spectral Regrowth– The only concern of the spectral regrowth in the

transmitter amplifiers is with the nonlinearity that generates distortion products within adjacent and alternate channels

• If pass-band of the transmitter is a small percentage of the carrier frequency, the nonlinearity can be characterized by odd-order terms of a power series or by a Fourier sine series

– See Figures 5.6 and 5.7– See Equations 5.4.2 through 5.4.6

Transmitter System Analysis and DesignAdjacent and Alternate Channel Power

Multitone Techniques

• Two-tone measurements are commonly used in determining the intermodulation distortion characteristics

• In digital mobile communications, signals are more complicated and their spectral regrowthcannot be accurately analyzed in terms of the two-tone IMD– It becomes necessary to apply the multitone signals

to analytically asses the ACPR of tranmission signals– The n-tone ACPR formula is found in equation 5.4.7

• This does not work for alternate channel power regrowth as it is mainly caused by fifth order nonlinear distortion of the PA

Transmitter System Analysis and DesignAdjacent and Alternate Channel Power

ACPR of Cascaded Stages in Transmitter Chain

• The ACPR of a transmitter consisting of multiple stages connected in cascade can be derived in terms of 5.4.13 and the cascaded OIP3 formula

Transmitter System Analysis and DesignNoise-Emission Calculation

Formula• The noise emission from mobile station transmitters is one of the

important specifications of the transmitter– Especially the noise emission in the receiver band of a full-duplex

mobile station. – The noise emissions discussed here are those located outside of

alternate channels• Formulas for Noise-Emission Calculation

– Begin with estimate of contribution from an individual stage in the transmitter chain

– The Noise Factor is F– The equivalent device noise at the input port is

• P_Nd=P_No*(F-1)– Therefore the noise generated at its output port is

• P_Ndout = g * kTo * (F-1)– In addition to this noise, if an input noise is imporsed on the input of the

device, the total output power becomes• P_Nout = g * P_Nin + g * kTo *(F-1)

Transmitter System Analysis and DesignNoise-Emission Calculation

Formula

• For a transmitter consisting of n stages, the noise emission has a similar formula– P_Nout = g_tx * P_Nin + g_tx * kTo *(F_tx-1)– Where g_tx is overall transmitter gain– And where F_tx is the overall noise factor of the transmitter

Transmitter System Analysis and DesignNoise-Emission Calculation

Output Noise of an Attenuator

• General Expression

• It may cause some confusion when we calculate output noise of a loss device such as an attenuator– While thermal noise kTo is imposed at the

input of an attenuator – the noise at the output of this attenuator is kTo

)1(0__ −⋅⋅+⋅= FgkTPgP inNoutN

Transmitter System Analysis and DesignNoise-Emission Calculation

Output Noise Floor of Device or Transmitter

• Minimum Input Noise of a Device is the thermal noise kTo

Transmitter System Analysis and DesignTransmitter Chain Gain Distribution and Performance

• See spreadsheets

Applications of System Design

• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Applications of System DesignSelection of Frequency Plan

• For Superheterodyne architecture – this amounts to:– Understanding the Frequency Band Allocation

(Regulation)– Selection of the receive IF frequency

• Resulting determination of the transmit IF• Resulting determination of the LO

– Need to do a spur analysis• Understand mixer spurs• Understand harmonics of power amplifiers• Understand IMs of power amplifiers in multicarrier

applications– Need to define filter requirements for spurs

Applications of System DesignReceiver System Design

Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation and Noise Figure

• Determine required receiver sensitivity• Determine required receiver NF• Assemble line-up of elements within the receiver

and determine the cascaded NF and the corresponding various component gain and NFs– DESIGN is an iterative process

• Select Components from catalog of available parts• Develop components as required• Ensure sensitivity requirements are satisfied

• Keep in mind degradations in receiver sensitivity due to output power spectrum in receive band

Applications of System DesignReceiver System Design

Linearity and Third-Order Intercept Point

• Compute cascaded IIP3 (or OIP3) for line up on receiver units.

• Consider filtering of intermodulationproducts when evaluating gain of intermodulation products and corresponding IIP3 levels

• Determine if intermodulation power:– Poses threat as interference– Results in distortion

Applications of System DesignReceiver System Design

Selectivity and Blocking Performance

• Selectivity– Design channel filters so that desired signal

passes “undistorted” and adjacent/alternate channels are rejected

• Parameters include:– Insertion Loss– Passband flatness– Passband gain slope– Passband group delay and group delay slope– Out of band rejection– Spuriuos rejection

Applications of System DesignReceiver System DesignADC Dynamic Range

• Develop line up of units in receiver• Determine input power range• Determine signal level through transceiver

– Target acceptable range of levels of input for ADC to work properly

– Determine to what degree ALC is required• ALC=automatic level control. e.g. VGA with

feedback control

VGA in Superheterodyne Full-Duplex Receiver

Applications of System DesignReceiver System Design

System Line-Up Analysis and Design

• Clearly the system line-up is a key component of the system design– Allow for “drop in” of available units– Track:

• Signal strength• Noise Power• Cascaded Noise Figure• Cascaded IIP

– Note:• Spurious frequencies• LO power level• Channel selectivity (filter) requirements• Input signal power• Threshold BER

Applications of System DesignReceiver System Design

Gain Control and RSSI Accuracy• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Applications of System DesignTransmitter System Design

Transmission Power

• Transmission Power of Transceiver is combined with Antenna Gain to give EIRP– Key parameter in link– Establishes (largely) the DC power

requirements of transceiver– Establishes thermal design (if applicable)– Cost driver

• Cornerstone of transmitter design

Applications of System DesignTransmitter System Design

Adjacent and Alternate Channel Power

• Significant concern of transmitter is spectral regrowth and resulting undesired power in adjacent or alternate channels– Interference to other users of system– Drives linearity concerns in transmitter design

• Cascaded IIP is typical quantity tracked• AM/AM and AM/PM characteristics provide details as to

regrowth– Post amplifier filters may be used to limit out of band

power• At expense of insertion loss and wasted DC power• At expense of thermal design for high power transmitters

Applications of System DesignTransmitter System Design

Noise and Spurious Emission in a Receiver Band

• Significant signal level differences between receive and transmit signals– e.g. ~-100 dBm vs. 30 dBm

• Design must ensure adequate rejection of noise and spurious signals in receive band– Degrades receiver sensitivity– May damage RF front end (due to overdrive)

Applications of System DesignTransmitter System Design

Spectrum of Burst Ramp-Up and –Down Transients• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Applications of System DesignTransmitter System Design

Residual Amplitude Modulation• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Applications of System DesignTransmitter System Design

Modulation Accuracy• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Applications of System DesignTransmitter System Design

Radio Frequency Tolerance• Selection of Frequency Plan• Receiver System Design

– Determination of Carrier-to-Noise Ratio for Receiver Performance Evaluation– Noise Figure– Linearity and Third-Order Intercept Point– Selectivity and Blocking Performance– ADC Dynamic Range– System Line-Up Analysis and Design– Gain Control and RSSI Accuracy

• Transmitter System Design– Transmission Power– Adjacent and Alternate Channel Power– Noise and Spurious Emission in a Receiver Band– Spectrum of Burst Ramp-Up and –Down Transients– Residual Amplitude Modulation– Modulation Accuracy– Radio Frequency Tolerance

Homework

• Review material• Refine spreadsheets• A design problem will be prepared and

distributed next week which we will work on for remainder of class.