SL6649-1
3115 - 4.1
SL6649-1
200MHz DIRECT CONVERSION FSK DATA RECEIVER
The SL6649-1 is a low power direct conversion radio
receiver for the reception of frequency shift keyed
transmissions. It features the capability of 'power down' for
battery conservation.
The device also includes a low battery flag indicator.
FEATURES
I
Very Low Power Operation - typ. 3.7mW
I
Single Cell Operation with External Inverter
I
Complete Radio Receiver in One Package
I
Operation up to 200MHz
I
100nV Typical Sensitivity
I
Operates up to 1200 BPS
I
On Chip Tunable Active Filters
I
Minimum External Component Count
I
Low Power Down Current Typical 5µA
PIN
1
2
3
4
5
6
7
8
9
10
11
12
13
14
DESCRIPTION
1
2
3
4
5
6
7
8
9
10
11
12
13
14
28
27
26
25
24
23
22
21
20
19
18
17
16
15
MP28
PIN
28
27
26
25
24
23
22
21
20
19
18
17
16
15
DESCRIPTION
CHANNEL B TEST.
LO INPUT CHANNEL B
LO INPUT CHANNEL A
V
CC
1 (MIXER)
MIXER I/P A
MIXER I/P B
CHANNEL A TEST
LO CURRENT SOURCE
RFA II (EMIT) RF DEC
RFA II (BASE) RF INPUT
RF DEC
RF O/P
COLPITTS OSC O/P DISABLE
NC
APPLICATIONS
I
Low Power Radio Data Receiver
I
Wristwatch Credit Card Pager
I
Radio Paging
I
Ultrasonic Direction Indication
I
Security Systems
I
Remote Control Systems
ABSOLUTE MAXIMUM RATINGS
Supply Voltage
Storage Temperature
Operating Temperature
6V
-55°C to +150°C
-20°C to +70°C
GND
BATTERY ECON
GYRATOR CURRT ADJ
REF VOLTAGE
BANDGAP REF VOLT
V
CC
2
BIT RATE FILTER
DATA OUTPUT
GND
NC
NC
NC
BATT FLAG INPUT
BATT FLAG OUTPUT
N.B. It is advisable to connect NC pins to ground.
Figure 1: Pin Connections - Top View
ORDERING INFORMATION
SL6649-I/KG/MPES
- Small outline (MP28) supplied in tubes
SL6649-1/KG/MPEF - Small outline (MP28)
supplied in tape & reel
1
SL6649-1
TYPICAL ELECTRICAL CHARACTERISTICS
These characteristics are guaranteed by design.
T
amb
= 25°C, V
CC
1 = 2.5V, V
CC
2 = 3.5V
Value
Characteristic
RF Amplifier
Noise Figure
Power Gain
Input Impedance
Mixer
RF Input Impedance
LO Input Impedance
LO DC Bias Voltage
Detector
Output Current
Colpitts Oscillator
Frequency
Output Voltage
Pin
Min
Typ
5.5
14
19
23, 24
26, 27
26, 27
7
±4
Max
Units
dB
dB
Conditions
RS = 50Ω
See Fig. 8
See Figs. 9 (a) and (b)
See Fig. 10
Equal to pin 25
V
µA
16
16
15
20
kHz
mVp-p
R = 270K, Pin 3 to GND
R
L
>> 1MΩ N.B. Refer to Channel
Filter Fig. 4
RECEIVER CHARACTERISTICS (GPS DEMONSTRATION BOARD)
Measurement conditions (unless otherwise stated):
Applications circuit diagram Fig.6; V
CC
1 = 1.3V; V
CC
2 = 2.3V; T
amb
=
25°C; Colpitts oscillator resistor = 270kΩ; mixer input A and B phase balance = 180°; local oscillator input A and B phase
balance = 90°. Measurement methods as described by CEPT Res 2 specification. F
IN
= 153MHz (512 baud).
Value
Characteristic
Terminal Sensitivity Tone
only 4/5 call reception
Deviation Acceptance
Centre Frequency Acceptance
Adjacent Channel Rejection
Adjacent + 1 Channel Rejection
Third Order Intermod adj-1 + adj-2
±2.0
65
65
52
Min
Typ
-127
±2.5
±2.5
70
70
53
Max
-124
Units
dBm
kHz
kHz
dB
dB
dB
Conditions
∆f
= 4.5kHz, R
S
= 50Ω
3dB De-Sensitisation. F
IN
= F
LO
∆f
= 4.5kHz
Figure 2: Block Diagram of SL6649-1 Direct Conversion Receiver
∆f
= 4.5kHz Channel Spacing
25kHz
External capacitors on test
pins A and B.
3
SL6649-1
PRINCIPLE OF OPERATION
The incoming signal is split into two parts and frequency
converted to baseband. The two paths are produced in phase
quadrature (see Fig 2) and detected in a phase detector which
provides a digital output. The quadrature network must be in
the local oscillator path.
At a data rate of 512 baud and a deviation frequency of
4.5kHz, the input to the system has a demodulation index of 18.
This gives a spectrum as in Fig 3. f
1
and f
0
represent the ‘steady
state’ frequencies (i.e. modulated with continuous ‘1’ and ‘0’
respectively). The spectrum in Fig 3 is for reversals (a
0-1-0-1-0-1 etc. pattern) at the system bit rate; f
C
is the nominal
carrier frequency).
When the LO is at the nominal carrier frequency, then a
continuous ‘0’ or ‘1’ will produce an audio frequency, at the
output of the mixers corresponding to the difference between f
0
and f
C
or f
1
and f
C
. If the LO is precisely at fc, then the resultant
output signal will be at the same frequency regardless of the
data state; nevertheless, the relative phases of the two paths
will reverse between ‘0’ and ‘1’ states. By applying the amplified
outputs of the mixers to a phase discriminator, the digital data is
reproduced.
Figure 3: Spectrum Diagram
TUNING THE CHANNEL FILTERS
The adjacent channel rejection performance of the
SL6649-1 receiver is determined by the channel filters. To
obtain optimum adjacent channel rejection, the channel filters’
cut off frequency should be set to 8kHz. The process tolerances
are such that the cut off frequency cannot be accurately
defined, hence the channel filters must be tuned. However the
receiver characteristics on the previous page can be achieved
with a fixed 270kΩ resistor between pin 3 and GND.
Tuning is performed by adjusting the current in the gyrator
circuits. This changes the values of the gyrator’s equivalent
inductance. The cut off frequency is tuned to 8kHz. To
accurately define the cut off of the channel filters, a gyrator
based Colpitts oscillator circuit has been included on the
SL6649-1. The Colpitts oscillator and channel filters use the
same type of architecture, hence there is a direct correlation
between oscillator frequency and cut off frequency. By knowing
the Colpitts oscillator frequency the channel filter cut off
frequency can be estimated from Figure 4.
Once the channel filters have been tuned it may be
necessary to disable the Colpitts oscillator. The Colpitts
oscillator is disabled by connecting the Colpitts oscillator
output/disable pin (pin # 16) to V
CC
2. This is needed since the
Colpitts oscillator may impair the performance of the receiver.
k
k
Figure 4
k
Figure 5: Channel Filter Response
4
MCU
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