Philips Semiconductors
Product specification
Low-voltage mixer FM IF system
SA676
DESCRIPTION
The SA676 is a low-voltage monolithic FM IF system incorporating a
mixer/oscillator, two limiting intermediate frequency amplifiers,
quadrature detector, logarithmic received signal strength indicator
(RSSI), voltage regulator and audio and RSSI op amps. The SA676
is available in a 20-pin SSOP (shrink small outline package).
The SA676 was designed for cordless telephone applications in
which efficient and economic integrated solutions are required and
yet high performance is desirable. Although the product is not
targeted to meet the stringent specifications of high performance
cellular equipment, it will exceed the needs for analog cordless
phones. The minimal amount of external components and absence
of any external adjustments makes for a very economical solution.
PIN CONFIGURATION
DK Package
RF IN+ 1
RF IN– DECOUPLING 2
OSC
OUT
3
OSC
IN
4
RSSI OUT 5
V
CC
6
AUDIO FEEDBACK 7
AUDIO OUT 8
RSSI FEEDBACK 9
QUADRATURE IN 10
20 MIXER OUT
19 IF AMP DECOUPLING
18 IF AMP IN
17 IF AMP DECOUPLING
16 IF AMP OUT
15 GND
14 LIMITER IN
13 LIMITER DECOUPLING
12 LIMITER DECOUPLING
11
LIMITER OUT
FEATURES
•
Low power consumption: 3.5mA typical at 3V
•
Mixer input to >100MHz
•
Mixer conversion power gain of 17dB at 45MHz
•
XTAL oscillator effective to 100MHz (L.C. oscillator or external
oscillator can be used at higher frequencies)
SR00514
Figure 1. Pin Configuration
•
102dB of IF Amp/Limiter gain
•
2MHz IF amp/limiter small signal bandwidth
•
Temperature compensated logarithmic Received Signal Strength
Indicator (RSSI) with a 70dB dynamic range
•
Audio output internal op amp
•
RSSI output internal op amp
•
Internal op amps with rail-to-rail outputs
•
ESD protection: Human Body Model 2kV
Robot Model 200V
•
Low external component count; suitable for crystal/ceramic/LC
filters
APPLICATION
•
Cordless phones
ORDERING INFORMATION
DESCRIPTION
20-Pin Plastic Shrink Small Outline Package (Surface-mount)
TEMPERATURE RANGE
-40 to +85°C
ORDER CODE
SA676DK
DWG #
SOT266-1
BLOCK DIAGRAM
20
19
18
17
16
15
14
13
12
11
IF
AMP
MIXER
RSSI
LIMITER
QUAD
OSCILLATOR
+ –
V
REG
E
B
– +
AUDIO
1
2
3
4
5
6
7
8
9
10
SR00515
Figure 2. Block Diagram
1993 Dec 15
6–129
853-1726 11659
Philips Semiconductors
Product specification
Low-voltage mixer FM IF system
SA676
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
CC
T
STG
T
A
θ
JA
Single supply voltage
Storage temperature range
Operating ambient temperature range
Thermal impedance
DK package
PARAMETER
RATING
7
–65 to +150
–40 to +85
117
UNITS
V
°C
°C
°C/W
DC ELECTRICAL CHARACTERISTICS
V
CC
= +3V, T
A
= 25
°
C; unless otherwise stated.
LIMITS
SYMBOL
V
CC
I
CC
PARAMETER
Power supply voltage range
DC current drain
TEST CONDITIONS
MIN
2.7
3.5
SA676
TYP
MAX
7.0
5.0
V
mA
UNITS
AC ELECTRICAL CHARACTERISTICS
T
A
= 25°C; V
CC
= +3V, unless otherwise stated. RF frequency = 45MHz; +14.5dBV RF input step-up; IF frequency = 455kHz; R17 = 2.4kΩ
and R18 = 3.3kΩ; RF level = –45dBm; FM modulation = 1kHz with
±5kHz
peak deviation. Audio output with de-emphasis filter and C-message
weighted filter. Test circuit Figure 3. The parameters listed below are tested using automatic test equipment to assure consistent electrical
characteristics. The limits do not represent the ultimate performance limits of the device. Use of an optimized RF layout will improve many of
the listed parameters.
SYMBOL
PARAMETER
TEST CONDITIONS
LIMITS
MIN
TYP
100
100
7.0
f1 = 45.0; f2 = 45.06MHz
Input RF level = –52dBm
Matched 14.5dBV step–up
50Ω source
RF input resistance
RF input capacitance
Mixer output resistance
IF section
IF amp gain
Limiter gain
AM rejection
Audio level
SINAD sensitivity
THD
S/N
Total harmonic distortion
Signal–to–noise ratio
IF RSSI output, R
9
= 2kΩ
1
RSSI range
IF input impedance
IF output impedance
Limiter input impedance
Limiter output impedance
Limiter output voltage
Pin 18
Pin 16
Pin 14
Pin 11
Pin 11
1.3
1.3
No modulation for noise
IF level = –110dBm
IF level = –50dBm
50Ω source
50Ω source
30% AM 1kHz
Gain of two
IF level –110dBm
60
44
58
50
120
17
–55
60
0.5
1.7
70
1.5
0.3
1.5
0.3
130
.90
2.2
dB
dB
dB
mV
dB
dB
dB
V
V
dB
kΩ
kΩ
kΩ
kΩ
mV
RMS
(Pin 20)
1.25
Single–ended input
10
–10
17
+2.5
8
3.0
1.5
4.0
MAX
UNITS
Mixer/Osc section (ext LO = 220mV
RMS
)
f
IN
f
OSC
Input signal frequency
Crystal oscillator frequency
Noise figure at 45MHz
Third–order input intercept point (50Ω
source)
Conversion power gain
MHz
MHz
dB
dBm
dB
dB
kΩ
pF
kΩ
1993 Dec 15
6–130
Philips Semiconductors
Product specification
Low-voltage mixer FM IF system
SA676
AC ELECTRICAL CHARACTERISTICS
SYMBOL
RF/IF section (int LO)
System SINAD sensitivity
PARAMETER
(Continued)
TEST CONDITIONS
MIN
RF level = –114dBm
LIMITS
TYP
12
MAX
dB
UNITS
NOTE:
1. The generator source impedance is 50Ω, but the SA676 input impedance at Pin 18 is 1500Ω. As a result, IF level refers to the actual signal
that enters the SA676 input (Pin 18) which is about 21dB less than the “available power” at the generator.
CIRCUIT DESCRIPTION
The SA676 is an IF signal processing system suitable for second IF
systems with input frequency as high as 100MHz. The bandwidth of
the IF amplifier and limiter is at least 2MHz with 90dB of gain. The
gain/bandwidth distribution is optimized for 455kHz, 1.5kΩ source
applications. The overall system is well-suited to battery operation
as well as and high quality products of all types.
The input stage is a Gilbert cell mixer with oscillator. Typical mixer
characteristics include a noise figure of 7.0dB, conversion gain of
17dB, and input third-order intercept of –10dBm. The oscillator will
operate in excess of 100MHz in L/C tank configurations. Hartley or
Colpitts circuits can be used up to 100MHz for xtal configurations.
The output impedance of the mixer is a 1.5kΩ resistor permitting
direct connection to a 455kHz ceramic filter. The input resistance of
the limiting IF amplifiers is also 1.5kΩ. With most 455kHz ceramic
filters and many crystal filters, no impedance matching network is
necessary. The IF amplifier has 44dB of gain and 5.5MHz
bandwidth. The IF limiter has 58dB of gain and 4.5MHz bandwidth.
To achieve optimum linearity of the log signal strength indicator,
there must be a 12dB(v) insertion loss between the first and second
IF stages. If the IF filter or interstage network does not cause
12dB(v) insertion loss, a fixed or variable resistor or an L pad for
simultaneous loss and impedance matching can be added between
the first IF output (Pin 16) and the interstage network. The overall
gain will then be 90dB with 2MHz bandwidth.
The signal from the second limiting amplifier goes to a Gilbert cell
quadrature detector. One port of the Gilbert cell is internally driven
by the IF. The other output of the IF is AC-coupled to a tuned
quadrature network. This signal, which now has a 90° phase
relationship to the internal signal, drives the other port of the
multiplier cell.
The demodulated output of the quadrature drives an internal op
amp. This op amp can be configured as a unity gain buffer, or for
simultaneous gain, filtering, and 2nd-order temperature
compensation if needed. It can drive an AC load as low as 10kΩ
with a rail-to-rail output.
A log signal strength indicator completes the circuitry. The output
range is greater than 70dB and is temperature compensated. This
signal drives an internal op amp. The op amp is capable of
rail-to-rail output. It can be used for gain, filtering, or 2nd-order
temperature compensation of the RSSI, if needed.
NOTE: dB(v) = 20log V
OUT
/V
IN
1993 Dec 15
6–131
Philips Semiconductors
Product specification
Low-voltage mixer FM IF system
SA676
C26
R18
3.3k
R17
2.4k
FLT1
C23
C21
FLT2
C18
C17
C15
20
19
18
17
16
15
14
13
12
11
IF
AMP
MIXER
LIMITER
RSSI
QUAD
OSCILLATOR
+–
V
REG
–+
1
C1
2
3
4
5
6
7
R11
10k
8
9
10
C9
C12
C8
L1
C2
C7
C10
C5
L2
45MHz
INPUT
C6
X1
C19
390pF
R10
10k
C27
2.2µF
R19
11k
IFT1
C14
RSSI
OUTPUT
V
CC
AUDIO
SA676DK Demoboard
Application Component List
C1
C2
C5
C6
C7
C8
C9
C10
C12
C14
C15
C17
C18
C19
C21
51pF NPO Ceramic
220pF NPO Ceramic
100nF +10% Monolithic Ceramic
5-30pF trim cap
1nF Ceramic
10.0pF NPO Ceramic
100nF +10% Monolithic Ceramic
10
µ
F Tantalum (minimum) *
2.2µF +10% Tantalum
100nF +10% Monolithic Ceramic
10pF NPO Ceramic
100nF +10% Monolithic Ceramic
100nF +10% Monolithic Ceramic
390pF +10% Monolithic Ceramic
100nF +10% Monolithic Ceramic
C23
C26
C27
FLT 1
FLT 2
IFT 1
L1
L2
X1
R5
R10
R11
R17
R18
R19
100nF +10% Monolithic Ceramic
100nF +10% Monolithic Ceramic
2.2µF Tantalum
Ceramic Filter Murata SFG455A3 or equiv
Ceramic Filter Murata SFG455A3 or equiv
330
µ
H TOKO 303LN-1130
330nH Coilcraft UNI-10/142-04J08S
0.8
µ
H nominal TOKO 292CNS-T1038Z
44.545MHz Crystal ICM4712701
Not Used in Application Board (see Note 8, pg 8)
8.2k +5% 1/4W Carbon Composition
10k +5% 1/4W Carbon Composition
2.4k +5% 1/4W Carbon Composition
3.3k +5% 1/4W Carbon Composition
11k +5% 1/4W Carbon Composition
SR00516
* NOTE: This value can be reduced when a battery is the power source.
Figure 3. SA676 45MHz Application Circuit
1993 Dec 15
6–132
Philips Semiconductors
Product specification
Low-voltage mixer FM IF system
SA676
RF GENERATOR
45MHz
SA676 DEMOBOARD
RSSI
AUDIO
V
CC
(+3)
DE-EMPHASIS
FILTER
DC VOLTMETER
C–MESSAGE
SCOPE
HP339A DISTORTION
ANALYZER
SR00517
Figure 4. SA676 Application Circuit Test Set Up
NOTES:
1. C-message: The C-message and de-emphasis filter combination has a peak gain of 10 for accurate measurements. Without the gain, the
measurements may be affected by the noise of the scope and HP339A analyzer. The de-emphasis filter has a fixed -6dB/Octave slope
between 300Hz and 3kHz.
2. Ceramic filters: The ceramic filters can be 30kHz SFG455A3s made by Murata which have 30kHz IF bandwidth (they come in blue), or
16kHz CFU455Ds, also made by Murata (they come in black). All specifications and testing are done with the wideband filter.
3. RF generator: Set your RF generator at 45.000MHz, use a 1kHz modulation frequency and a 6kHz deviation if you use 16kHz filters, or
8kHz if you use 30kHz filters.
4. Sensitivity: The measured typical sensitivity for 12dB SINAD should be 0.45µV or –114dBm at the RF input.
5. Layout: The layout is very critical in the performance of the receiver. We highly recommend our demo board layout.
6. RSSI: The smallest RSSI voltage (i.e., when no RF input is present and the input is terminated) is a measure of the quality of the layout and
design. If the lowest RSSI voltage is 500mV or higher, it means the receiver is in regenerative mode. In that case, the receiver sensitivity
will be worse than expected.
7. Supply bypass and shielding: All of the inductors, the quad tank, and their shield must be grounded. A 10-15µF or higher value tantalum
capacitor on the supply line is essential. A low frequency ESR screening test on this capacitor will ensure consistent good sensitivity in
production. A 0.1µF bypass capacitor on the supply pin, and grounded near the 44.545MHz oscillator improves sensitivity by 2-3dB.
8. R5 can be used to bias the oscillator transistor at a higher current for operation above 45MHz. Recommended value is 22kΩ, but should not
be below 10kΩ.
1993 Dec 15
6–133
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