Texas Instruments TRF1500 User Manual

Evaluation Board Documentation

TRF1500 Integrated Dual-Band RF Receiver User’s Guide

APPLICATION BRIEF: SWRA004A

Wireless Communications Business Unit

Digital Signal Processing Solutions July 98

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Contents

Abstract.........................................................................................................................9

Product Support .........................................................................................................10

The TI Advantage Extends Beyond RF to Every Other Major Wireless System

Block.......................................................................................................................10

Related Documentation...........................................................................................11

World Wide Web.....................................................................................................11

Email.......................................................................................................................11

Introducti on.................................................................................................................12

Design Considerations...............................................................................................13

External Components..............................................................................................13

Board Design and Impedance Matching..................................................................13

TRF 1500 Dual-Band Receiver ...................................................................................14

TRF1500 Control State ...............................................................................................17

Low Band Cascaded Receiver Section: LNA, External SAW Filter, Mixer, and LO

Buffer Amplifier...........................................................................................................18

Low-Band LNA........................................................................................................19

Low-Band LNA Turn on Time..................................................................................19

Low-Band LNA Input...............................................................................................20

Low-Band LNA Output............................................................................................20

Surface Acoustic Wave (SAW) Filter.......................................................................21

Low-Band Mixer......................................................................................................22

Low-Band Mixer RF Input .......................................................................................22

Low-Band Mixer LO Input .......................................................................................23

Low-Band IF Output................................................................................................23

Low-Band LO Buffer Amplifier Output.....................................................................24

Low-Band Cascaded Test Guide ...............................................................................26

LOW-Band Cascaded: Power Conversion Gain......................................................26

Low-Band Cascaded: Power Conversion Gain Reduction.......................................27

Low-Band Cascaded: Noise Figure.........................................................................28

Low-Band Cascaded: RF Input Return Loss...........................................................30

Low-Band Cascaded: LO Input Return Loss...........................................................30

LOW BAND: LO Buffer Out pu t Power.....................................................................31

Low-Band: Power Leakage LO In to RF In..............................................................31

Low-Band Cascaded: Third Order Input Intercept Point (IIP3).................................32

Low-Band Cascaded: 1dB RF Input Compression Point.........................................33

Low-Band Cascaded: 1dB Blocking Point...............................................................34

High-Band Cascaded Receiver Section: LNA, Mixer, LO Buffer Amplifier .............35

Cascaded High-Band Receiver Section: LNA, Mixer, and LO Amplifier...................35

High-Band RF Input................................................................................................36

High-Band LO Input................................................................................................36

High-Band IF Output...............................................................................................38

High-Band LO Buffer Amplifier Output ....................................................................39

High-Band Cascaded Test Guide...............................................................................40

High-Band Cascaded: Power Conversion Gain.......................................................40

Contents

High-Band Cascaded: Power Conversion Gain Reduction......................................41

High-Band Cascaded: Image Rejection...................................................................42

High-Band Cascaded: Noise Figure........................................................................43

High-Band Cascaded: RF Input Return Loss ..........................................................44

High-Band : LO Bu ffer Out pu t Power.......................................................................45

High-Band Cascaded: Power Leakage LO In to RF In ............................................46

High-Band Cascaded: Third Order Input Intercept Point (IIP3)................................46

High-Band Cascaded: 1dB Input Compression Point..............................................47

High-Band Cascaded: 2X2 Spur Performance........................................................48

High Band: 3X3 Spur Performance.........................................................................49

Low-Band and High-Band Transmit ..........................................................................50

Low- and High-Band Transmit Mixer.......................................................................50

Low-Band and High-Band Transmit Mixer RF Input ................................................50

Low- and High-Band Transmit Mixer IF Output .......................................................51

Low-Band Transmit Mixer Test Guide.......................................................................52

Low-Band Transmit Mixer: Power Conversion Gain................................................52

Low-Band Transmit Mixer: Noise Figure .................................................................53

Low-Band Transmit Mixer: Input Return Loss..........................................................54

Low-Band Transmit Mixer: Power Leakage LO In to TX In......................................55

Low-Band Transmit Mixer: Power Leakage TX In to LO In......................................55

Low-Band Transmit Mixer: 1dB Input Compression Point .......................................56

Low-Band Transmit Mixer: Second Order Input Intercept Point (IIP2).....................57

Low-Band Transmit Mixer: Third Order Input Intercept Point (IIP3).........................58

High-Band Transmit Mixer Test Guide......................................................................59

Low-Band LNA Stand-Alone Test Guide...................................................................60

Low-Band LNA: Gain ..............................................................................................60

Low-Band LNA: Input Return Loss..........................................................................60

Low-Band LNA: Output Return Loss.......................................................................61

Low-Band LNA: Isolation.........................................................................................61

Low-Band LNA: 1dB Input Compression Point ........................................................61

Low-Band LNA: Noise Figure..................................................................................62

Low-Band LNA: Third Order Input Intercept Point (IIP3)..........................................63

Low-Band Receiver Mixer Stand-Alone Test Guide .................................................65

Low-Band Receiver Mixer: Power Conversion Gain................................................65

Low-Band Receiver Mixer: Input Return Loss.........................................................66

Low-Band Receiver Mixer: Power Leakage LO In to RF In......................................67

Low-Band Receiver Mixer: Noise Figure.................................................................67

Low-Band Receiver Mixer: 1dB RF Input Compression Point..................................69

Low-Band Receiver Mixer: Third Order Input Intercept Point (IIP3).........................70

Appendix A: Test Bench Configuration.....................................................................72

Figures

Figure 1. TRF1500 Dual-Band Receiver Block Diagram................................................14

Figure 2. Cascaded Block Diagram of the Low-Band Receiver Section.........................18

Figure 3. Voltage Divider at Low-Band LNA Input..........................................................19

Figure 4. Low- Ba nd LN A In pu t Co n figur ation...................................................................20

Figure 5. Low- Ba nd LN A Ou tp ut C onfi gur a ti o n.................................................................21

Figure 6. SA W Filter Inserti o n Loss..................................................................................21

Figure 7. Low-Band Mixer RF Input Configuration ............................................................22

Figure 8. Low-Band Mixer LO Input Configuration............................................................23

Figure 9. Low-Band IF Output Configuration....................................................................24

Figure 10. Low-Band Buffer Amplifier Output Configuration .............................................25

Figure 11. Block Diagram of the High-Band Receiver Section..........................................35

Figure 12. High-Band RF Input Configuration...................................................................36

Figure 13. High-Band LO Frequency Doubler Driven Configuration .................................37

Figure 14. High-Band LO Directly Driven Configuration....................................................37

Figure 15. High-Band IF Output Configuration..................................................................38

Figure 16. High-Band LO Buffer Amplifier Output Configuration.......................................39

Figure 17. Transmit Mixer Block Diagram.........................................................................50

Figure 18. Low- and High-Band Transmit Mixer RF Input Configuration...........................51

Figure 19. Low- and High-Band Transmit Mixer IF Output Configuration..........................51

Figure 20. Test Bench Setup: Power Conversion Gain, Power Conversion Gain

Reduction, 1dB RF Input Compression Point, Second Order Input Intercept Point (IIP2), 2x2 Spur Perform ance, 3x3 Spur Performance, Ima ge rej ec tion

and LO Buffer Output Power...........................................................................72

Figure 21. Test Bench Setup: Third Order Input Intercept Point (IIP3), 1dB Blocking

Point Measurements.......................................................................................72

Figure 22. Test Bench Setup: Noise Figure .....................................................................73

Figure 23. Test Bench Setup: Power Leakage LO In to RF In .........................................73

Figure 24. Test Bench Setup: Power Leakage RF In to LO In Measurements.................74

Figure 25. Test Bench Setup: LNA Noise Figure Measurements .....................................74

Figure 26. Test Bench Setup: LNA Third Order Input Intercept Point (IIP3) Measurement75

Figure 27. Test Bench Setup: LNA 1dB Input Compression Point...................................75

Tables

Table 1. Pin Descriptions.................................................................................................15

Table 2. Control State and the Corresponding Active Circuits.........................................17

Table 3. LB LNA, LB Mixer, SAW Filter, and LB IF Amp Parameters...............................26

Table 4. HB LNA, HB mixer, HB IF amp..........................................................................40

Table 5. Low-Band Transmit Performance Parameters...................................................52

Table 6. High-Band Transmit Mixer Performance Parameters.........................................59

Table 7. Low-Band LNA Parameters...............................................................................60

Table 8. Low-Band Receiver Mixer Parameters..............................................................65

TRF1500 Integrated Dual-Band RF

Abstract

Receiver User’s Guide

The dual-band handset market is expanding very rapidly due to the increase in customers requiring roaming capa bility. The customer also demands that handsets have an increase in features while keeping the size compact. These dual-band handset requirements put pressure on the integrated circuit manufacturer to be innovative while keeping costs low.

To meet this demand, Texas Instruments (TI) has developed the TRF1500 receiver. The TRF1500 is a fully-integrated dual-band receiver in a single package. The selection of the external components and the layout of the system board required to complete a tr ans ceiver des ign are cri ti c al t o achi eve maxim um perform ance.

This application report discusses the implementation and impedance matching of each section of the TRF1500 to keep the required board area to a minimum and minimizing external components while maximizing performance. It also discusses parameter measurement techniques.

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 9

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Product Suppor t

The TI Advan ta ge E xt en ds Be yon d RF to E very Other Major Wireless System Block

Speaker

Audio

Interface

Microphone

SINGLE CHIP ANAL OG

BASEBAND

TMS320C54X

DSP Core

S/W

ASIC

TSC6000

SINGLE CHIP DIGIT AL BASE BAND

ARM7TDMIE

BACKPLANE

Microcontroller

ARM7TDMIE

(C470)

S/W

Interface

User Display

Keyboard

SIM Card

Receiver

TRF1xxx

Synthesizer

TRF2xxx

Modulator

Modulator TRF3xxx

TRF3xxx

RF SE CTION

Op Amps

Switches

Regulators

POW E R MGMT

Power A mp

TRF7xxx,

TRF8xxx

Digital Baseband

TI’s single-chip Digital Baseband Platform, combines two high-performance core processors – a digital signal processor tailored for digital wireless applications and a microcontroller designed specifically for low-power embedded systems. The customizable platform helps wireless digital telephone manufacturers lower component counts, save board space, reduce power consumption, introduce new features, save development costs and achieve faster time to market, at the same time giving them flexibility and performance to support any standard worldwide.

Analog Baseband

TI analog baseband components provide a Mixed-signal bridge between the real world of analog si g nal s an d di gi t al sig nal pr ocessors, the key en abli n g t ec hnology of the digital wireless industry. Using a seamless architecture for wireless communications technology, TI matches its baseband interfaces, radio frequency ICs and power managem en t I Cs to digital signal pr ocessing engines t o cre at e complete DSP Solutio ns for digital wireless systems.

Power Management

TI provides power management solutions with integration levels designed to meet the needs of a ran ge o f wireless applicatio ns . From di s cr et e LD Os an d v olt a ge supervisors to complete power supplies for the baseband section, TI power ma nagement solutions play an important role in increasing wireless battery life, time-to-market and system functionality.

For more information visit the Wireless Communications web site at www.ti.com/sc/docs/wireless/home.htm.

10 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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Related Documentation

The following list specifies product names, part numbers, and literature numbers of corresponding TI documentation.

Dual-Band/Dual-Mode PCS Receiver

❑

SLWS041A

World Wide Web

Our World Wide Web site at www.ti.com contains the most up to date product information, revisions, and additions. Users registering with TI&ME can build custom information pages and receive new product updates automatically via email.

For technical issues or clarification on switching products, please send a detailed email to sc-infomaster@ti.com. Questions receive prompt attention and are usually answered within one business day.

, Literature number

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 11

Introduc ti on

SWRA004A

The TRF1500 is a dual-band/dual-mode Personal Communications Syste m (PCS) receiver for cellular telephones operating dual mode (a nalog and digital) in the 800 MHz band and single mode (digital) in the 1900 MHz band. The TRF1500 consists of a low noise amplifier (LNA) and mixer for each band. For image rejection, the low-ba nd receiver relies on an off-chip image rejection filter between the LNA and mixer while the highband receiver uses an image rejection mixer. The device operates from a single 3.75 volt supply and is controlled by six digital CMOS control lines. The digital control offers a wide range of control states, including a sleep mode where the device typically

draws less than 5µA. Additionally, the local o scillator (LO) inputs have buffered outputs

that can be used in either single-ended or differential mode for a phase-locked-loop (PLL) configuration. A state is also available that allows the low-band LO to serve as the high-band LO through a mode-selectable frequency doubler.

A wide-ba nd mix er is als o avai l a bl e for tr ansm i t loo p ar chi t ec t ur es which are commonly used in advanced mobile phone systems, global systems for mobile communications and other digital systems.

The TRF1500 is available in a 48-pin plastic thin quad flatpack package and is characterized for operation from -40C to 85C operatin g fr ee- ai r tem p er ature.

Please refer to the data sheet for the TRF1500 (TI literature number SLWS041A) for detailed information on the device specifications and refer to the users guide for test instructions (TI literature number SWRA004A).

12 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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Design Conside ra ti ons

The successful integration of a TRF1500 receiver device into a design is dependent upon the performance of the external components and the quality of the board design and layout.

Ex ternal Componen ts

Componen t tolerance and Q specifications (where applicable) should be obs er ve d dur i n g the selecti o n o f any exte rnal components. The TRF1500 data sheet, TI literature number SLWS041A, includes a Bill of Mate rials (BOM) detailing components with proven performance, that are used on the evaluation board. The location and orientation of components should also be taken into consideration for maximum performance and manufacturability. For e xamp le, the lo w-ba nd imag e rejection is dependent on an external Surface Acoustic Wave (SAW) component. This filter is used to reject signal outside the band of the receiver and has bee n chosen to maximize the TR F1500 performance, while maintaining minimum size and cost.

Board Design and Impedance Matching

The quality of the board layout is also critical to the TRF1500 performance. Co rrect transmission line impedances must be maintained throughout the design to insure maximum performance. Co rrect transmission line impedances can be maintained by using proper line widths and board stack-up in relation to the dielectric constant of the board material.

Utilizing the correct external component to match the device impedance to board transmission line impedance is also very important.

For measurement simplicity, the e valuation board utilizes RF Balun transformers for impedance matching selected differential inputs and outputs to single-ended inpu ts and outputs. Please note that the Baluns are used only for evaluating the device on the evaluation board and do not have to be included in the end user’s application.

To minimize unwanted signal interference and coupling, digital lines should be routed around and away from the receiver. On a multi-layer board, running a separate plane for the digital lines is highly recommended. Power supply lines should be filtered and regulate d as clo se as poss ible at the device term i nal.

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 13

TRF 1500 Dual-Band Receiver

A block diagram of the TRF1500 dual-band receiver front end down converter is shown in Figure 1. Pin names and descriptions are provided in Table 1. The device operates from a single 3.75 volt supply and its operation is controlled by 6 digital CMOS control lines the TRF1500 operates in 18 different states. The control codes and the corresponding active circuits are given in Table 2.

Figure 1. TRF1500 Dual-Band Receiver Block Diagram

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14 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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Table 1. Pin Descriptions

Pin Number Name Description

1 Bias Adjust Bias adjust 2 TX IF + Transmit IF, noninverting output 3 TX IF - Transmit IF, inv er ting output 4 GND ground 5 MIX IN LOW BAND Low band mixer input 6 GND ground 7VCC Vcc 8 GND Ground

9 TX + Transmit, noninverting input 10 TX - Transmit, inverting input 11 GND Ground 12 IR ADJUST D Image rejection adjustment 13 HI/LO High band/low band select 14 SYN ON VCO power control 15 HIGH BAND IF + High band IF noninvert ing output 16 HIGH BAND IF - High band IF, inver ting output 17 LOW BAND IF + Low band IF noninverting output 18 LOW BAND IF - Low band IF, inverting output 19 GND ground 20 HIGH BAND LO + High band noninverting LO output 21 HIGH BAND LO - High band, inv erti ng LO out put 22 LOW BAND LO + Low band noninverting LO output 23 LOW BAND LO - Low band, inv er ting LO output 24 RX ON Low noise amplifier/mixer power control 25 VCC Vcc 26 TX ON Transmit mixer/driver power control 27 HIGH BAND LO IN -/RF GND High band LO inverting input/RF GND 28 HIGH BAND LO IN + High band LO noninverting input 29 GND ground 30 DOUDLER TANK Doubler output 31 VCC VCC 32 LOW BAND LO IN Low band LO input 33 GND ground 34 GND ground 35 X2 ON Doubler power control 36 IR ADJUST A Image rejection adjustm ent 37 IR ADJUST B Image rejection adjustm ent

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 15

38 STRONG SIGNAL Strong signal indication 39 GND ground 40 VCC VCC 41 GND ground 42 LNA IN HIGH BAND High band LNA input 43 LNA IN LOW BAND Low band LNA input 44 GND ground 45 LNA OUT LOW BAND Low band LNA output 46 GND ground 47 GND ground 48 IR ADJUST C Image rejection adjustment

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TRF1500 Control State

The TRF1500 operates in 18 different states: The control code and active circuits are given in Table 2.

Table 2. Control State and the Corresponding Active Circuits

Control Code

(HI/LO, SYN ON, RX ON, TX ON, STRONG SIGNAL, X2)

000000 Sleep Mode 010000 Low-Band LO Input Buffer On LB LO Buffer 011000 Low-Band Receive Normal LB LO Buffer, LB LNA, LB Mixer 011010 Low-Band Receive Strong Signal LB LO Buffer, LB Mixer 010100 Low-Band Transmit Mixer LB LO Buffer, LB TX Mixer 011100 Low-Band Receive and Transmit Mixer LB LO Buffer, LB LNA (On High), LB Mixer , LB TX

011110 Low-Band Transmit Mixer LB LO Buffer, LB LNA (On High), LB Mixer 010001 Doubler On LB LO Buffer, Frequency Doubler, HB LO Buffer 011001 Low-Band Receive Normal, Doubler On

011011 Low-Band Receive Strong Signal, DoublerOnLB LO Buffer, LB Mixer, Fr equenc y Doubler

011111 Low-Band Transmit, Doubler On LB LO Buffer, LB LNA (On High), LB Mixer, LB TX

111011 High-Band Receive Strong Signal, DoublerOnHB LO Buffer, HB Mixer, Fr equenc y Doubler

110000 High-Band LO Input B uff er On HB LO Buffer 111000 High-Band Receive Normal HB LO Buffer, HB LNA, HB Mixer 111010 High-Band Receive Strong Signal HB LO Buffer, HB Mixer 111001 High-Band Receive Frequency, Doubler On LB LO Buff er, HB LO Buffer, HB LNA, HB Mixer,

110100 High-Band Transmit Normal HB LO Buffer, HB TX Mixer 110101 High-Band Transmit Frequency, Doubler

Active Circuits

Mixer

LB LO Buffer, LB LNA, LB Mixer, F r equenc y Doubler

Mixer

Frequency Doubler

HB LO Buffer, HB TX Mixer, Frequency Doubler, LB LO Buffer

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 17

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Low Band Cascaded Receiver Section: LNA, External SAW Filter, Mixer, and LO Buffer Ampli f ier

The TRF1500 low-band receiver section, shown in Figure 2, is an integrated front-end down converter designed to operate in the 800 MHz frequency range. The low-band down converter consists of an LNA, mixer, LO buffer amplifier and an off-chip image reject filter. The digital control allows the low-band to operate in thre e different states to compensate for the environment in which the TRF1500 is operating. The device can be operated in the normal state, where the LNA, mixer and buffer amplifier are on, the strong signal state, where the LNA is off and the mixer and buffer amplifier are on, or the transmit state, where the LNA bias current is increased to prevent compression when the transmitter is on.

The low-band receiver has low typical current consumption of 21mA at 3.75V supply. The cascaded gain is typically 26dB while providing good dynamic range with approximately a -10dBm third order input intercept point (IIP3). The low-band receiver has a typical system noise figure of approximately 2.5 dB for excellent sensitivity.

Figure 2. Cascaded Block Diagram of the Low-Band Receiver Section

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Low-B an d LNA

In a typical down-conversion receiver, the LNA is usually placed directly after the antenna and a band-select filter. The purpose of the LNA is to amplify the desired signal being received while adding as little undesired noise and distortion as possible. The TRF1500 LNA is a common emitter amplifier, designed to operate on a single 3.75 volt supply. The LNA has two selectable gain states, normal state or strong signal state, which are controlled with the digital CMOS control lines. The strong signal state, which disables the LNA, is provided for operation in a high signal environment such as near the base station. Operating near the base station in the normal state could cause an increase in the intermodulation product levels and thus cause undesired noise and distortion in the receiver. Stand-alone LNA performance can be ascertained by reconfiguring the evaluation board as noted on the da tashee t.

Low-B an d LNA Turn on Tim e

The turn on time can be adjusted by changing the values of C10, R6 and R7, as shown in Figure 3 and Figure 4. The resistors form a voltage-divider network across the supply, Vcc. The function of this network is to provide a bias condition near the ideal operating region at the base of the common emitter amplifier. By providing this bias condition, the charge time of the series capacitor, C10, can be ad justed. Changing the value of resistors should not affect gain, IIP3 or noise figure (NF) performance.

Figure 3. Voltage Divider at Low-Band LNA Input

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 19

Low-B an d LNA Input

Figure 4 details the lo w-band LNA input configuration. The LNA input impedance matching network primarily determines the cascaded gain, noise figure, and input return loss performance of the low-band receiver section. A simple high-pass shunt-L (L10) impedance matching network is used for optimum noise figure performance. The trade off for this optimization is a lower input return loss in the pass-band, but with sufficient attenuation in the stop-band. C10 has minimal effect on matching and is used mainly to optimize the turn-on time.

Figure 4. Low-Band LNA Input Configuration

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Low-B an d LNA Output

Figure 5 details the LNA output configuration. The LNA output impedance matching network has several functions. The matching network optimizes the third order input intercept point (IIP3) performance while also matching the LNA output impedance to the Surface Acoustic W a ve (SAW) filter input impedance. A shunt-C (C11) is used to match the LNA output to the SAW filter input. Increasing the value of the shunt capacito r will improve the gain and noise f igu re performance but will degrade the third order input intercept point. The end user can adjust the LNA input and output mat chi n g network to optimize a particular parameter of interest.

20 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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Figure 5. Low-Band LNA Output Configuration

Surface Aco us tic Wave (SAW) Filter

The SAW filter is used primarily as an image-reject filter (IRF). The i m age frequency (f frequency (f

). The image frequency acts as an interferer to the system.

) plus two times the IF frequ ency (fIF); fIM = fCH + (2 x

During the down-conversion process, the image and the desired channel are both converted to a common IF. Left unfiltered, the image could completely mask the desired signal. The IRF rejects this image before the RF signal is introduced to the mixer.

) is located at the desired channel

By minimizing the image before it reaches the mixer, the sensitivity of the receiver is enhanced. To further minimize potential interferers, a band-select filter is typically used at the front of the receiver, before the LNA. The band-select filter passes only those frequencies that fall within the system receive band. In many TDMA systems, the duplexor acts as the band-select filter.

The off-c hip SAW image- r eject filter used on the TR F1 500 applications board has a 3dB nominal insertion loss and a 25 MHz bandwid th at a c en ter fr eq uency of 880 MHz as shown in Fi gur e 6.

Figure 6. SAW Filter Insertion Loss

SAW Filter Insertion Loss

-5

-10

-15

-20

-25

-30

-35

-40

Insertion Loss (dB)

-45

-50

-55

-60

860

Frequency (M Hz)

900

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 21

Low-Band Mixer

SWRA004A

The purpose of the mixer in a down-conversion receiver is to translate incoming signals from one frequency to another. The low-band mixer in the TRF1500 is a three port high-side injected circuit. The mixer takes two known input signals, a radio frequency (RF) signal and a local oscillator (LO) signal and mixes them together to create a sum and difference intermediate frequency (IF). High-side injection means the LO is higher in frequency than the RF by the IF frequency. The output of the mixer is the IF and contains the difference and the sum of the RF and LO signals.

The difference of the RF and LO signals is the desired IF frequency in a down-conversion receiver. The undesired signal, the sum of the RF and LO frequencies, can be attenuated by using a low pass filter. The low-band mixer section of the TRF1500 is a Gilbert cell design with open collector outputs. The Gilbert cell structure was used for its robust isolation and harmonic suppression characteristics.

The TRF1500 mixer typically achieves a noise figure of 7.5 dB with an input third order intercept point of 3.5 dBm. Stand-alone mixer performance can be ascertained by reconfiguring the evaluati on board as noted on the dat ash eet.

Low-Band Mixe r RF Input

Figure 7 details the mixer RF input configuration. The signal from the LNA passes through the external image-reject SAW filter and back into the device’s low-band mixer input terminal (MIX_IN_LOW_BAND). Minimal mixer input impedance matching is required. A high-pass shunt-L (L11) and series-C (C13) network are used for impedance matching the SAW filter output to the mixer RF input. The shunt inductor presents a short at the IF frequency. This configuration minimizes the IF leakage and prevents unwanted interfering signals at, or near, the IF frequency from degrading the mixer’s noise figure performance.

Figure 7. Low-Band Mixer RF Input Configuration

22 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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Low-Band Mixer LO Input

Figure 8 details the low-band mixer LO input configuration. The input power range level for the LO buffer amplifier is flexible enough (-3 dBm to -7 dBm) to drive the mixer without entering compression. The LO signal is injected through an internal LO buffer amplifier and into the mixer. A high pass shunt-L (L14) and series-C (C17) network is used for impedance matching. The inductor also shunts to ground any un desired noise that could be injected to the mixer.

Figure 8. Low-Band Mixer LO Input Configuration

Low -Band IF Ou tput

Figure 9 details the low-band IF output configuration. The lowband mixer has a differential IF output with a 1kΩ differential

output impedance. For evaluation, a 16:1 transformer balun, with a insertion loss of 1.8 dB, is used to transform the 1kΩ differential output to a single-ended output which is then matched to 50Ω. In

the actual application, the IF output is usually connected to a narrow band channel select filter with a differential input and the transformer balun is not required.

The supply voltage (VCC) is applied to the IF pins with pull up inductors (L12, L13). A low-pass filter network is provided prior to the balun. The filter also acts as part of the impedance matching network. During optimization of the output matching network, it was found that mismatching the differential output, accomplished with C55, gives the best IIP3 performance with minimum effect on the gain and noi se figure performance. C5 5 als o hel ps to decouple the digital CMOS control line from the LO signal. The IF response is shaped by the shunt-L (L51) after the transformer balun. L51 is also used to block unwanted noise that could be reflect ed back to the mi xer . T he s eri es ca pac i t or (C51) ne ar t he LB_IF_OUT port is used as a dc block for evaluation purposes and does not have to be implemented in the end-users system.

TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide 23

Figure 9. Low-Band IF Output Configuration

Low-B an d LO B uf fer Am pl i fie r Ou tp ut

SWRA004A

Figure 10 details the low-band LO buffer amplifier configuration. The low-band LO buffer amplifier can be used in either singleended or differential mode for a phase lock loop (PLL) configuration. The buffer is digitally controlled and requires a operating drive level ranging from -3 to -7 dBm. Fo r evaluation purposes, a 1:1 transformer balun, with an insertion loss of 2.7 dB, is used to convert the differential output to a single-ended output. The series capacitors at the buffer output are used for dc blocking.

The transmission line on the output of the buffer amplifier are used to convert the 100Ω differential to 50Ω differential.

The transmission lines on the output of the buffer amplifier can be modeled as microstrip lines. The values used for the calculations depend on the PCB substrate, the board stackup and the required impedance. The physical dimensions of the microstrip lines can be calculated using standard microstrip transmission line equations using the following values:

Frequency = 990 MHz ER = 4.400 (FR4), Height = 12.0000 m ils , Thickness = 1.5000

mils (Copper) Electrical Parameters: ZO = 35.350 Ohms, E_EFF = 90.000 Physical Parameters: Width = 37.777 mils , Length = 1613.305 mils

24 TRF1500 Integrat ed Dual- B and RF Receiver User’s Guide

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