CML Microcircuits CMX7031 Istruzioni per l'installazione e il funzionamento

Application Note

CMLMicrocircuits

COMMUNICATION SEMICONDUCTOR

CMX7031:

An Example Core Design for a

Complete Family Radio

AN/2WR/7031/FRS/3 July 2007

1 Introduction

The CMX7031 is a highly integrated baseband processor that is targeted at analog two way radio

applications. Professional and leisure radio designs can benefit from the extensive functionality, low

power consumption, and aggressive pricing offered by the CMX7031. Additionally, the ability to

enhance its functions through updated Function Imagefiles allows the CMX7031 to offer enhanced

features for no additional cost.

The purpose of this application note is to illustrate how the CMX7031 can be configured for a feature

rich “family radio” product. This document will describe how the CMX7031 can be configured to

perform the following functions:

 Half Duplex voice communications

 Text Messaging (both open and private messages)

 GPS location data

 Unique ‘ring tones’

 Audible alerting tones, for example indicating when a button has been pressed

 ‘All Call’ (urgent) call capability

 RF Synthesizer configuration

 System clock configuration

This document reflects the CMX7031 device functionality after being loaded with Function Image 1.3.

Use of this document with other Function Imagesmay result in undesired operation. Discussion of

Function Imageloading procedures is beyond the scope of this document and is fully discussed in

the CMX7031 datasheet.

The following information should be consulted while reviewing this application note:

1. CMX7031 Datasheet

2. CMX7031 User Manual

3. CMX7031 Synthesizer Calculator Application Note and Spreadsheet

Application Note CMX7031: An Example Core Design for a Complete Family Radio

Table of Contents

1Introduction.....................................................................................................................................1

2CMX7031 Function Image1.3 Feature Set.................................................................................3

3Description of Scenario ..................................................................................................................4

3.1 Transmit Functions................................................................................................................4

3.2 Receive Functions.................................................................................................................5

3.3 Assumptions ..........................................................................................................................6

3.4 Block Diagram .......................................................................................................................7

4CMX7031 Functional Considerations.............................................................................................8

4.1 RF Considerations.................................................................................................................8

4.2 ADC Considerations..............................................................................................................9

4.3 DAC Considerations............................................................................................................11

4.4 System Clock Generator Considerations ............................................................................11

4.5 FFSK / MSK Considerations................................................................................................13

4.6 Transmit Signal Level Considerations.................................................................................14

4.6.1 Transmit Audio Path Considerations...............................................................................14

4.6.2 Tx Limiter Calculations....................................................................................................15

4.6.3 CTCSS Tone Transmit Calculations ...............................................................................16

4.6.4 MSK and Inband Tone Transmit Signal Calculations .....................................................16

4.7 Receive Signal Level Considerations..................................................................................16

4.7.1 Receive Audio Path Considerations................................................................................16

4.7.2 CTCSS Signal Detection Threshold Calculations...........................................................17

4.7.3 MSK and Inband Signal Detection Threshold Calculations ............................................18

5Operating States...........................................................................................................................18

5.1 STATE 0 and STATE 1: Initial States..................................................................................19

5.2 STATE 2: Setup...................................................................................................................19

5.3 STATE 3: Sleep...................................................................................................................21

5.4 STATE 4: RX Startup...........................................................................................................22

5.5 STATE 5: Ring Tone Tx.......................................................................................................23

5.6 STATE 6: Voice Rx..............................................................................................................24

5.7 STATE 7: FFSK / MSK Rx...................................................................................................24

5.8 STATE 8: FFSK / MSK Tx...................................................................................................25

5.9 STATE 9: Voice Tx..............................................................................................................26

5.10 STATE 10: Monitor..............................................................................................................27

6Conclusion....................................................................................................................................27

Application Note CMX7031: An Example Core Design for a Complete Family Radio

2 CMX7031 Function Image1.3 Feature Set

In addition to being backward compatible with previous Function Images, Function Image1.3 loads

the following functions into the CMX7031:

Base configuration

 Single channel half duplex operation

 Three analogue inputs with input amplifier and programmable gain adjustment for connection

to microphone and demodulator sections

 Transmit output drivers with programmable level adjustment for single point, two point, and

I / Q modulation.

 Flexible Rx input signal routing

Audio processing

 Tx channel filtering for 12.5kHz and 25kHz bandwidths

 Tx signal limiting (software adjustable)

 Rx channel filtering (300Hz HPF and 2.55kHz / 3.0kHz LPF)

 Preemphasis and deemphasis

 Companding

 Scrambling (frequency inversion with adjustable split point)

 Digital gain adjustment

 Audio output with digital gain adjustment

 Selectable order of signal processing blocks

Subaudio signalling

 CTCSS encoder / decoder (preprogrammed with 51 tones, plus user programmable tone)

 DCS encoder / decoder (programmable 23/24 bit)

Inband signalling

 XTCSS encoder/decoder

 Programmable Selcall encoder / decoder

 Programmable audio tone generator (for custom audio tones)

 DTMF encoder

Data modem

 1200 / 2400 baud FFSK / MSK modem

o Data packet mode incorporating interleaving, FEC, CRC and data scrambler

(functions that are suitable for text messaging / paging, caller identification, caller

location, digital poll of remote radio location, GPS information in NMEA 0183 format,

general data transfer)

o Free format mode

 1200 bps FSK modem for Marine VHF applications

NOAA Weather Radio (for USA and Canada applications)

 WAT detector (Warning Alert Tone, 1050Hz)

 SAME (Specific Area Message Encoding) preamble / end-of-frame detector and data

demodulator

Auxiliary

 2 programmable system clock outputs (384kHz – 20MHz)

 2 auxiliary ADCs with four selectable input paths

 4 auxiliary DACs (one with configurable auto ramping profile)

 2 GPIO pins (can be used as Tx enable and Rx enable signals)

 2 flexible Integer-N RF synthesizers (100MHz – 600MHz) with phase detectors and charge

pumps

Application Note CMX7031: An Example Core Design for a Complete Family Radio

3 Description of Scenario

This document will use a combination of a state diagram and pseudocode routines to describe how

the CMX7031 can be configured to perform tasks for a possible application. In this “system” we will

assume that two hand held FRS radios are being used, both of which are equipped with the

CMX7031. The following functions are required:

 Half duplex voice communications

 Text Messaging (both ‘open’ and ‘private’ messages)

 GPS location data

 Unique ‘ring tones’ (single tones and simple melodies)

 ‘All Call’ (urgent) call capability

Clearly the CMX7031 could be used to implement many more radio designs, however this document

is not intended to describe all options but to provide a detailed overview of what is required in

software to control the CMX7031.

For engineers who have other requirements and wish to discuss them further or who wish to receive

further clarification on the information in this document, please contact the CML Help Desk for your

respective geographic area:

North and South America [email protected]

China [email protected]

Southeast Asia [email protected]

Europe, Africa, Australia and Asia [email protected]

3.1 Transmit Functions

The FRS radio in this application is configured to transmit on FRS channel 1 (462.5625MHz). The

radio user presses the “Push To Talk” (PTT) radio button to begin a voice transmission to the second

remote radio. When the PTT button is pressed:

1. If the user has previously configured a “buddy list” in a software look up table, they can scroll

through the list and highlight the person(s) they wish to call before pressing the PTT button.

This will allow the host microcontroller to reconfigure the CMX7031 for the appropriate Tx

channel and CTCSS tone frequency.

2. An audible alerting tone should be generated so the user knows a button was pressed.

3. After the audible alerting tone is generated, the CMX7031 can be used to process the

transmitted speech (e.g. preemphasis). The CMX7031 can also generate and transmit a

subaudio tone (i.e. CTCSS tone) for remote receiver squelch control.

The user can press the “Poll” button to manually request the location data of the remote user. When

the “Poll” button is pressed:

1. An audible alerting tone will be generated by the CMX7031 so the user knows a button was

pressed.

2. The CMX7031 will transmit an FFSK / MSK data burst to the remote user. This FFSK / MSK

data burst will instruct the remote user to transmit its location data back to the calling radio.

The user can send a text message to a remote user by entering text on the FRS radio and pressing

the “Send” button.

1. The user will select the ‘text message’ function (the activation of the ‘text message’ function is

not described in this document).

2. The user selects the intended recipient of the message and indicates whether the message is

‘open’ or ‘private’.

 If the user has previously configured a “buddy list”, the user can scroll through this list

and highlight the desired message recipient(s).

Application Note CMX7031: An Example Core Design for a Complete Family Radio

3. The user can compose the text message by one of the two following methods:

 Preset text messages. The user can scroll through a list of preprogrammed text

messages stored on the host microcontroller and highlight the desired message.

 User typed text messages. The user enters the desired text through the radio’s

keypad.

4. Once these steps are performed and the “Send” button is pressed, the host microcontroller

and CMX7031 can generate an FFSK / MSK data burst containing both the recipient’s

address and the actual message data.

If a received message has errors, the radio can use its CMX7031 to transmit a “retransmission

request” via an FFSK / MSK data burst to the remote radio.

3.2 Receive Functions

In this application, either voice or FFSK / MSK data can be received.

The FRS radio, configured to receive on FRS channel 1 (462.5625MHz), will normally be in “sleep”

mode waiting to receive a call. The CMX7031’s ADC1 monitors the RSSI signal from the RF

transceiver. An incoming transmission will cause the RSSI signal to exceed the ADC’s “high”

threshold and cause an interrupt to be generated. The host microcontroller should then read the

STATUS ($C6) and AUXADC1 DATA ($A9) registers to ensure that the source of the interrupt was a

rising RSSI signal. Once the IRQ source has been verified as RSSI, the CMX7031 should be

configured for both voice and FFSK / MSK reception.

The next IRQ should indicate the type of incoming call:

 If STATUS ($C6) b11 = 1, CTCSS detection has occurred and a voice call is imminent.

 If STATUS ($C6) b4 = 1, 2400 bps FFSK / MSK has been detected and a data burst is

imminent.

If the incoming transmission is a voice call, the CMX7031 will:

 Generate a ring tone to alert the user that a call is about to be heard.

 Process the recovered voice signal for presentation to the external speaker driver.

If the incoming transmission is FFSK / MSK data, the host microcontroller will interpret the received

FFSK / MSK message and proceed accordingly.

The user can press the radio’s “Monitor” button to listen for all activity on a channel. When this

happens:

1. An audible alerting tone will be generated by the CMX7031 so the user knows a button was

pressed.

2. The CMX7031 will activate its audio output amplifier to allow any received signal to be passed

to the radio’s speaker or headset.

Application Note CMX7031: An Example Core Design for a Complete Family Radio

3.3 Assumptions

The following assumptions were used in the development of this application note:

 VDD = 3.3V provided by three “AAA” batteries (3 cells x 1.5V / cell = 4.5V nominal).

o Low dropout regulator used to step down battery voltage for CMX7031.

o “Low Battery Warning” at 3.6V (arbitrarily chosen).

o Battery voltage scaled (60% reduction) prior to presentation to CMX7031 AUXADC4

input pin.

 FRS service with 25kHz channel spacing.

 External components configured in accordance with CMX7031 datasheet.

 19.2MHz TCXO supplies signals to both XTAL / CLK pin and RF CLOCK input (common to

both synthesizers). Baseband and RF clocks are derived from this 19.2MHz TCXO input.

 System Clock Generators

o Clock Output 1 = 12.288MHz

o Clock Output 2 = 16.384MHz

 Single point modulation used.

 Voice and CTCSS subaudio tone transmitted on MOD1.

o Voice + CTCSS output level = 500mVRMS

 Voice = 455mVRMS

 CTCSS = 45mVRMS

o Note: Actual voice and subaudio tone levels depend on VCO sensitivity and desired deviation; these

specifications are application dependent. A discussion of CMX7031 maximum signal levels is presented

later in the document.

 Voice:

o Preemphasis and deemphasis enabled

o Companding enabled

o Soft Limiter threshold = 525mVRMS

 Subaudio Tones:

o CTCSS subaudio tone is used during voice transmissions for squelch control.

 Tone # 20 (131.8Hz) generated during voice transmission.

 Tone # 1 (67.0Hz) detected during voice reception.

o No subaudio inversion.

 FFSK / MSK:

o Transmitted on MOD1 (no subaudio tone used for FFSK / MSK transmissions).

 MOD1 output level = 500mVRMS

o FFSK / MSK Address = 79 (arbitrarily chosen).

o 2400 bps, Type 5 message format.

o Frame length = 80 bytes (arbitrarily chosen).

o Standard scrambling seed.

o Default bit sync (0x5555) and frame sync (0xCB23) patterns are used

 Ring Tone

o 1250Hz ring tone is used in this scenario but the user can select different ring tones

or combinations of tones.

o Ring tone level = 500mVRMS

 RSSI signal monitored with ADC1 via AUXADC1 pin during sleep and Rx modes.

o High threshold (good carrier signal) = 1.85V for –60dBm received signal strength.

o Low threshold (indicates weak signal) = 0.9V for –100dBm received signal strength.

Note: The received signal strength values used for this document include no “noise margin”. The user

must evaluate their application and determine the optimal RSSI threshold and hysteresis settings.

 RF discriminator output is applied to CMX7031 DISC pin.

 CMX7031 AUDIOOUT pin delivers ring / alerting tones and recovered voice to an external

speaker driver amplifier for presentation to the radio speaker.

 RF Synthesizer

o FRS Channel 1 = 462.5625MHz, used for Tx and Rx.

o CMX7031 Channel 1 Synthesizer used for Tx RF upconversion.

o CMX7031 Channel 2 Synthesizer used for Rx downconversion.

Application Note CMX7031: An Example Core Design for a Complete Family Radio

 ADC (CMX7031 input pin names provided)

o AUXADC1: RSSI

o AUXADC2: Tx power amplifier temperature sensor input

o AUXADC3: TCXO temperature sensor input

o AUXADC4: Battery voltage

 DAC (CMX7031 output pin names provided)

o AUXDAC1: Tx power amplifier (ramp up / down profile)

 RAMDAC feature is used to take advantage of preprogrammed ramp profile.

o AUXDAC2: Tx power amplifier temperature compensation control voltage

o AUXDAC3: TCXO temperature compensation control voltage

o AUXDAC4: Not used

The normal operating mode for the CMX7031 in this application is powered down, monitoring RSSI

with ADC1 (STATE 3 from Figure 6).

3.4 Block Diagram

The following figure illustrates the CMX7031 and its interconnections as described in this application

note:

VCO

Loop

Filter

Tx PA

TCXO

LNA

LO1

Discriminator

70MHz

Crystal

Filter

450kHz

Ceramic Filter

CMX7031

DISC I/P

RF1+

CP1OUT

MOD 1

VCO Loop

Filter

RF2+

CP2OUT

RF CLOCK

XTAL/CLOCK

VDEC

to RF

circuitry

AUDIO O/P

MIC

SYS CLOCK2

SYS CLOCK1

AUXDAC4

AUXDAC3

AUXDAC2

AUXDAC1

AUXADC2

AUXADC1

AUXADC3

AUXADC4

RSSI

Tx PA Temperature

TCXO Temperature

Battery Voltage

12.288MHz

Tx PA Ramping

Tx PA Temp. Compensation

TCXO Temp. Compensation

16.384MHz

from

AUXDAC3

from

AUXDAC1

from

AUXDAC2

Unused

IRQ

REPLY DATA

CSN

CMD DATA

SERIAL CLOCK

Microcontroller

CBUS Interface

462.5625MHz

392.5625MHz

Figure 1: Application Scenario Block Diagram

Application Note CMX7031: An Example Core Design for a Complete Family Radio

4 CMX7031 Functional Considerations

4.1 RF Considerations

The CMX7031 includes two RF synthesizers that can be used to minimize external parts count and

BOM cost. These synthesizers are referred to as “Channel 1” and “Channel 2” in the CMX7031

documentation. While many different implementations are possible, the following scenario is used in

this document:

 Channel 1 Synthesizer

o Transmit mode, creates 462.5625MHz for FRS channel #1

 Channel 2 Synthesizer

o Receive mode, creates 392.5625MHz for LO1 (for RF downconversion of FRS

channel #1)

Once the desired frequencies are known, the “N” and “R” values for each synthesizer must be

calculated. CML has created a spreadsheet, “CMX7031 Synthesizer Calculator”, that can quickly

calculate N and R values for various requirements. This spreadsheet was used for the N and R

note is available upon request.

TCXO

VCO

Loop

Filter

Phase

Comparator

Internal to

CMX7031

External to

CMX7031

Charge

Pump

Fout

Fcomp

Figure 2: CMX7031 Synthesizer Block Diagram

The comparison frequency, Fcomp, was chosen to be 12.5kHz so an integer multiple relationship with

FRS channel frequencies could be achieved. (FRS channel spacing is 25kHz.) The following table

illustrates the register values needed to configure the CMX7031 Channel 1 Synthesizer to transmit on

FRS Channel 1.

Synthesized Frequency Register Contents

Tx N b9..0 0x408D

Tx N b19..0 0x4424

Tx R b9..0 0x4A00

462.5625MHz

(FRS Channel 1,

Transmit) Tx R b12..0 0x4C01

Table 1: RF Channel Data ($B2) Settings for Channel 1 Synthesizer

The second synthesizer in the CMX7031 is used to generate LO1 signal for the RF to IF1

downconversion. The following table illustrates the register values needed to configure the CMX7031

Channel 2 Synthesizer to generate this LO frequency:

Application Note CMX7031: An Example Core Design for a Complete Family Radio

Required LO1

Frequency Register Contents

Rx N b9..0 0x72AD

Rx N b19..0 0x741E

Rx R b9..0 0x7A00

392.5625MHz

(FRS Channel #1) Rx R b12..0 0x7C01

Table 2: RF Channel Data ($B2) Settings for Channel 2 Synthesizer

Channel 1 and Channel 2 Synthesizers each have “Tx” and “Rx” sections, but there is no requirement

that the “Tx” section actually be used for transmit operation. Bits 10..9 and 2..1 of RF Channel

Control ($B3) register determine which synthesizer settings (Tx or Rx) are enabled. The user is free

to select the channel and section for their particular application regardless of whether the device is in

transmit or receive mode.

4.2 ADC Considerations

The CMX7031 provides two 10-bit ADCs that are multiplexed between four different inputs. In this

application, the ADC inputs are used as follows:

 AUXADC1: RSSI

 AUXADC2: Input from Tx power amplifier temperature sensor

 AUXADC3: Input from TCXO temperature sensor

 AUXADC4: Battery voltage

In an actual application it would likely not be necessary to continuously monitor all four of these

parameters. For example, RSSI would not require monitoring during Tx mode, and Tx PA

temperature would not require monitoring during Rx mode. The host microcontroller can switch the

ADC multiplexer inputs to allow periodic monitoring of these parameters as necessary. This level of

control is application specific, however, and is therefore not discussed in this document.

The bit resolution of the ADCs in this application is:

bit

mV23.3

1023

V3.3

)12( V

DD 



The ADC input level range is 10% to 90% of VDD, which translates from 0.33V to 2.97V in this

application.

Rolling averaging is used with the CMX7031 ADCs in this application. With this averaging method, a

fraction of the current ADC input value will be added to the previously calculated ADC reading.

Programming register blocks P3.0 (ADC1) and P3.1 (ADC2) determine the scaling factors for the

current and previous ADC values; the values stored in these registers can vary from 0 to 8.

Application Note CMX7031: An Example Core Design for a Complete Family Radio

P3.0 or

P3.1

Value

Current

Value

Scale

Factor

Value

Scale

Factor

0 0.5 0.5

1 0.25 0.75

2 0.125 0.875

3 0.0625 0.9375

4 0.03125 0.96875

5 0.015625 0.984375

6 0.007813 0.992188

7 0.003906 0.996094

8 0.001953 0.998047

Table 3: ADC 'Rolling Averaging' Factors

For example, the default values for P3.0 and P3.1 are zero, and this corresponds to a 50% scaling

factor applied to each term:

(Current ADC Input x 0.5) + (Previous ADC Value x 0.5) = New ADC Reading

A value of 2 in P3.0 or P3.1 would result in:

(Current ADC Input x 0.125) + (Previous ADC Value x 0.875) = New ADC Reading

The chosen averaging value will directly impact the length of time required to achieve an accurate

reading. The following table illustrates the number of samples required to achieve 1% accuracy after

a large change of ADC input signal (e.g. 100% change). Smaller input signal changes will result in

faster convergence:

P3.0 or

P3.1

Value

Required

# of

samples

to achieve

<1% error

Time

required

to achieve

<1% error

(ms)

0 7 0.44

1 17 1.06

2 35 2.19

3 72 4.50

4 146 9.13

5 293 18.31

6 588 36.75

7 1177 73.56

8 2356 147.25

Table 4: Impact of ADC Averaging Lengths for Large Input Signal Changes

A tradeoff exists between response time and noise immunity, and the optimal averaging setting is

application dependent.

This application scenario monitors battery voltage so that the host microcontroller can be alerted to a

weak battery condition. The battery voltage will normally exceed the CMX7031 VDD of 3.3V, so the

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