MELEXIS TH7111 Datasheet

TH7111

868/915MHz

FSK/FM/ASK Receiver

Features

! Double superhet architecture for high degree of image rejection
! FSK for digital data and FM reception for analog signal transmission
! FM/FSK demodulation either with phase-coincidence or PLL demodulator
! Low current consumption in active mode and very low standby current
! Switchable LNA gain for improved dynamic range
! AFC feature allows wide carrier frequency acceptance range
! RSSI allows signal strength indication and ASK detection
! Surface mount package LQFP44

Ordering Information

Part No. Temperature Range Package

TH7111 -40 °C to 85 °C LQFP44

Application Examples

! General digital and analog 868 MHz or 915 MHz ISM band usage
! Low-power telemetry
! Alarm and security systems
! Keyless car and central locking
! Pagers

Technical Data Overview

! Input frequency range: 800 MHz to 930 MHz
! Power supply range: 2.5 V to 5.5 V for double conversion and 3.3 V to 5.5 V for single conversion
! Temperature range: -40 °C to +85 °C
! Operating current: 7.5 mA at low gain and 9.2 mA at high gain mode
! Standby current: < 100 nA
! Sensitivity: -109 dBm
! Sensitivity: -102 dBm
! Range of first IF: 10 MHz to 80 MHz
! Range of second IF: 455 kHz to 21.4 MHz
! Maximum input level: –10 dBm at ASK and 0 dBm at FSK
! Image rejection: > 65 dB (e.g. with SAW front-end filter and at 10.7 MHz 2
! Spurious emission: < -70 dBm
! Input frequency acceptance: ±50 kHz (with AFC option)
! RSSI range: 70 dB
! Frequency deviation range: ±5 kHz to ±120 kHz
! Maximum data rate: 80 kbit/s NRZ
! Maximum analog modulation frequency: 15 kHz

1)

at ± 8 kHz FSK deviation, BER = 3⋅10-3 and phase-coincidence demodulation

2)

at ± 50 kHz FSK deviation, BER = 3⋅10-3 and phase-coincidence demodulation

1)

with 40 kHz second IF filter BW (incl. SAW front-end filter loss)

2)

with 150 kHz second IF filter BW (incl. SAW front-end filter loss)

nd

IF)

TH7111 Data Sheet Page 1 of 20 Nov. 2001
3901007111 Rev. 005

TH7111

868/915MHz

FSK/FM/ASK Receiver

General Description

The TH7111 receiver IC consists of the following building blocks:

" PLL synthesizer (PLL SYNTH) for generation of the first and second local oscillator signals LO1 and LO2
" Parts of the PLL SYNTH are the high-frequency VCO1, the feedback dividers DIV_16 and DIV_2,

a phase-frequency detector (PFD) with charge pump (CP) and a crystal-based reference oscillator (RO)

" Low-noise amplifier (LNA) for high-sensitivity RF signal reception
" First mixer (MIX1) for down-conversion of the RF signal to the first IF (IF1)
" second mixer (MIX2) for down-conversion of the IF1 to the second IF (IF2)
" IF amplifier (IFA) to amplify and limit the IF2 signal and for RSSI generation
" Phase coincidence demodulator (DEMOD) with third mixer (MIX3) to demodulate the IF signal
" Operational amplifier (OA) for data slicing, filtering, ASK detection and automatic-frequency control (AFC)
" Bias circuitry for bandgap biasing and circuit shutdown

With the T H7111 receiver chip, various circuit c onfigurations can be arranged in order to m eet a number of
different custom er requirements . For FM/FSK reception the IF tank used in the phase coincidence dem odu­lator can be constituted either by a ceramic resonator or an LC tank (optionally with varactor to create an AFC
circuit). In PLL demodulator configuration, the multiplier MIX3 f orms a phase com parator. In ASK c onfigurati­on, the RSSI signal is feed to an ASK detector, which is c onstituted by the operational amplif ier. T he sec ond
VCO (VCO2) can be used either as the VCO of a PLL demodulator or as the LO 2 source of a second exter­nal PLL in a multi-channel system. The following table briefly summarizes the various configurations.

Single-conversion configuration Double-conversion configuration

FM/FSK

FM/FSK
FM/FSK
FM/FSK

ASK
ASK

The preferred superheter odyne configuration is double conversion where MIX1 and MIX2 are driven by the
internal local oscillator signals LO1 and LO 2, respectively. This allows a high degree of image rejection,
achieved in conjunction with an RF front-end filter. Eff icient RF front- end filtering is r ealized by using a SAW,
ceramic or helix filter in front of the LNA and by adding a LC filter at the LNA output.

It is also possible to use the T H7111 in single-conversion configur ation. This can be ac hieved by switching
the LO2 input of MIX2 from the on-chip PLL synthesizer to the pin IN_MIX2 by means of an internal switch
(done via pin SW_MIX2). Now MIX2 operates as an amplifier f or the IF1 signal if an external pull-down re­sistor at pin IN_MIX2 is added.

The same setting of MIX2 can be used for multi-channel applications. In this situation IN_MIX2 mus t be
driven by an external LO2 signal. This signal can be generated by the VCO2, which is mainly a bipolar tran­sistor that can be configured as a varactor-tuned VCO. Furthermore, a second external PLL for channel
selection via LO2 tuning is required. This may be arranged by using a PLL synthesizer chip that can be con­trolled through a 3-wire bus serial interface. The reference signal for the external PLL synthesizer can be
directly taken from the crystal-based reference oscillator RO.

narrow-band RX with ceramic demodulation
tank

wide-band RX with LC demod. tank and AFC wide-band RX with LC demod. tank and AFC
extended sensitivity RX with PLL demodulator extended sensitivity RX with PLL demodulator

RX with RSSI-based demodulation RX with RSSI-based demodulation

narrow-band RX with ceramic demodulation
tank

multi-channel RX with ceramic demodulation
tank and external channel synthesizer

RX with RSSI-based demodulation and exter­nal channel synthesizer

TH7111 Data Sheet Page 2 of 20 Nov. 2001
3901007111 Rev. 005

Block Diagram

TH7111

868/915MHz

FSK/FM/ASK Receiver

IN_DEM

OUT_IFA

19 20

18

RSSI

29

17

FBC1

16

IN_IFA

151413

VEE_IF

OUT_MIX2

VCC_MIX2

12

VCC_MIX1

11

IF1N

10

IF1P

9

VEE_MIX1

8

CAP_MIX1

7

VEE_LNA

5

IN_MIX1

6

OUT_LNA

43

31

32

OUTP

OUTN

28

27

OAP

OAN

26

OUT_OA

23

24

VCO2_E

VCO2_B

OA

VCO2

VCC_BIAS

25

VEE_BIAS

MIX3

BIAS

VREF

ENRO
ENRX

VCC_PLL

VEE_RO

VEE_PLL

30

37 144

36

34

IFA

RO

ROLF2 SW_MIX2

35

LF1

PFD

IF2

CP

LO2

MIX2MIX1

IF1

LO1

DIV_2

IN_MIX2

switch

DIV_16

VCO1

39 332221 38

GAIN_LNA

VEE_LNAC

2

LNA

IN_LNA

42

VCC_LNA41VEE_LNA

VEE_VCO1

43

40

Fig. 1: TH7111 block diagram

TH7111 Data Sheet Page 3 of 20 Nov. 2001
3901007111 Rev. 005

TH7111

868/915MHz

FSK/FM/ASK Receiver

Frequency Planning

Frequency planning is straightforward for single-conversion applications because there is only one IF that
might be chosen, and then the only possible choice is low-side or high-side injection of the LO1 s ignal (which
is now the one and only LO signal in the receiver).

The receiver’s double-conver sion architecture requires careful frequenc y planning. Besides the desired RF
input signal, there are a number of s purious signals that may cause an undesired response at the output.
Among them are the image of the RF signal (that must be suppressed by the RF front-end f ilter), spurious
signals injected to the first IF ( IF1) and their im ages which could be m ixed down to the sam e sec ond IF (IF2)
as the desired RF signal (they must be suppressed by the LC filter at IF1 and/or by low-crosstalk design).

By configuring the TH7111 for double conversion and using its internal PLL synthesizer with fixed feedback
divider ratios of N1 = 16 (DIV_16) and N2 = 2 (DIV_2) , four types of down-conversion ar e possible: low-s ide
injection of LO1 and LO2 (low - low), LO1 low-side and LO2 high-side (low-high), LO1 high-side and LO2
low-side (high-low) or LO1 and LO2 high-s ide (high-high). T he following table sum m arizes som e equations
that are useful to calculate the crystal reference frequency (REF), the firs t IF (IF1) and the VCO1 or firs t LO
frequency (LO1), respectively, for a given RF and second IF (IF2).

Injection type high-high low-low high-low low-high

REF (RF – IF2)/30 (RF – IF2)/34 (RF + IF2)/30 (RF + IF2)/34
LO1

32•REF 32•REF 32•REF 32•REF

IF1 LO1 – RF RF – LO1 LO1 – RF RF – LO1

LO2

2•REF 2•REF 2•REF 2•REF

IF2 LO2 – IF1 IF1 – LO2 IF1 – LO2 LO2 – IF1

The following table depicts generated, desired, pos sible images and som e undesired s ignals cons idering the
examples of 868.3 MHz and 915 MHz RF reception at IF2 = 10.7 MHz.

Signal type RF =

868.3 MHz

Injection type high-high
REF / MHz 28.58667

LO1 / MHz 914.77333
IF1 / MHz 46.47333
LO2 / MHz 57.17333
RF image/MHz 961.24667
IF1 image/MHz 67.87333

RF =

868.3 MHz

low-low

25.22353

807.15294

61.14706

50.44706

746.00588

39.74706

RF =

868.3 MHz

high-low low-high high-high

29.3 25.85294 30.14333

937.6 827.29412 964.58667

69.3 41.00588 49.58667

58.6 51.70588 60.28667

1006.9 786.28824 1014.17

47.9 62.40588 70.98667

RF =

868.3 MHz

RF = 915

MHz

RF = 915

MHz

low-low

26.59706

851.10588

63.89412

53.19412

787.21176

42.49412

RF = 915

MHz

high-low low-high

30.85667 27.22647

987.41333 871.24706

72.41333 43.75294

61.71333 54.45294

1059.83 827.49412

51.01333 65.15294

RF = 915

MHz

The selection of the ref erence crystal frequency is based on som e assumptions. As for example: the f irst IF
and the image frequencies should not be in a radio band where strong interfering signals might occur
(because they could represent parasitic receiving s ignals), the LO1 s ignal should be in the range of 800 MHz
to 915 MHz (because this is the optimum frequency range of the VCO1). Furtherm ore the first IF should be
as high as possible to achieve highest RF image rejection. The colum ns in bold depict the selec ted f r equenc y
plans to receive at 868.3 MHz and 915 MHz, respectively.

TH7111 Data Sheet Page 4 of 20 Nov. 2001
3901007111 Rev. 005

TH7111

868/915MHz

FSK/FM/ASK Receiver

Pin Definition and Descripti on

Pin No. Name I/O Type Functional Schematic Description

1 VREF analog

output

VREF

1

60k

reference voltage output,
approx. 1.23V

4 OUT_LNA analog

output

42 IN_LNA analog

input

2 VEE_LNAC ground

IN_LNA

42

5k

OUT_LNA

4

VEE_LNAC

2

LNA open-collector output,
to be connected to external
LC tank that resonates at RF

LNA input,
approx. 26Ω single-ended

ground of LNA core
(cascode)

3 GAIN_LNA analog

input

GAIN_LNA

3

400

Ω

LNA gain control (CMOS
input with hysteresis)

5 VEE_LNA ground LNA biasing ground
6 IN_MIX1 analog

input

7 CAP_MIX1 analog I/O

IN_MIX1

6

CAP_MIX1

7

Ω

13

Ω

13

500µA

40µA

Ω

330

MIX1 input, approx. 33Ω
single-ended

connection for MIX1
blocking capacitor

8 VEE_MIX1 ground MIX1 ground

20p

VCC

20p

IF1N

10

connected to external LC
tank that resonates at first IF

open-collector output, to be

9 IF1P analog I/O open-collector output, to be

IF1P

9

10 IF1N analog I/O

connected to external LC

VEE

2x500µA

VEE

tank that resonates at first IF

TH7111 Data Sheet Page 5 of 20 Nov. 2001
3901007111 Rev. 005

TH7111

868/915MHz

FSK/FM/ASK Receiver

Pin No. Name I/O Type Functional Schematic Description

11 VCC_MIX1 supply MIX1 positive supply

12 VCC_MIX2 supply MIX2 positive supply

13 OUT_MIX2 analog

output

OUT_MIX2

13

130

6.8k

Ω

230µA

MIX2 output, approx. 330Ω
output impedance

14 VEE_IF ground ground of MIX2, IFA and

DEMOD

2.2k

200µA

VCC

IFA input, approx. 2.2kΩ
input impedance

FBC1

16

IFA feedback capacitor

VEE

to be connected to external
IFA feedback capacitor

15 IN_IFA analog

VCC

input

IN_IFA

15

VEE

FBC2

17

VCC

2.2k

VEE

VEE

16 FBC1 analog I/O to be connected to external

17 FBC2 analog I/O

18 VCC_IF supply positive supply for IFA,

DEMOD and VCO2

19 OUT_IFA analog I/O

IFA output and MIX3 input
(of DEMOD)

OUT_IFA

19

40µA

20 IN_DEM analog

input

IN_DEM

20

47k

DEMOD input, to MIX3 core

21 SW_MIX2 digital

input

SW_MIX2

21

400

Ω

input selection for LO2 input
port of MIX2

TH7111 Data Sheet Page 6 of 20 Nov. 2001
3901007111 Rev. 005