SA676
Low-voltage mixer FM IF system
Rev. 3 — 19 July 2012
Product data sheet
1. General 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.
2. Features and benefits
Low power consumption: 3.5 mA typical at 3 V
Mixer input to > 100 MHz
Mixer conversion power gain of 17 dB at 45 MHz
XTAL oscillator effective to 100 MHz (LC oscillator or external oscillator can be used at
higher frequencies)
102 dB of IF amplifier/limiter gain
2 MHz IF amp/limiter small signal bandwidth
Temperature compensated logarithmic Received Signal Strength Indicator (RSSI) with
a 70 dB dynamic range
Low external component count; suitable for crystal/ceramic/LC filters
Audio output internal op amp
RSSI output internal op amp
Internal op amps with rail-to-rail outputs
ESD protection exceeds 2000 V HBM per JESD22-A114 and 1000 V CDM per
JESD22-C101
Latch-up testing is done to JEDEC Standard JESD78 Class II, Level B
3. Applications
Cordless telephones
NXP Semiconductors
SA676
Low-voltage mixer FM IF system
4. Ordering information
Table 1.
Ordering information
T
amb
=
40
C to +85
C
Type number
SA676DK/01
Topside
mark
SA676DK
Package
Name
SSOP20
Description
plastic shrink small outline package; 20 leads;
body width 4.4 mm
Version
SOT266-1
5. Block diagram
LIMITER_DECOUPL
LIMITER_DECOUPL
12
9
RSSI_FEEDBACK
IF_AMP_DECOUPL
IF_AMP_DECOUPL
20
19
18
17
16
15
14
13
IF amp
mixer
limiter
quad
OSC
RSSI
VREG
1
RF_IN
2
RF_IN_DECOUPL
E
3
OSC_OUT
B
4
OSC_IN
audio
5
RSSI_OUT
6
V
CC
7
AUDIO_FEEDBACK
8
AUDIO_OUT
002aag116
Fig 1.
Block diagram
SA676
All information provided in this document is subject to legal disclaimers.
QUADRATURE_IN
LIMITER_OUT
11
10
IF_AMP_OUT
MIXER_OUT
LIMITER_IN
IF_AMP_IN
GND
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 3 — 19 July 2012
2 of 22
NXP Semiconductors
SA676
Low-voltage mixer FM IF system
6. Pinning information
6.1 Pinning
RF_IN
RF_IN_DECOUPL
OSC_OUT
OSC_IN
RSSI_OUT
V
CC
AUDIO_FEEDBACK
AUDIO_OUT
RSSI_FEEDBACK
1
2
3
4
5
6
7
8
9
20 MIXER_OUT
19 IF_AMP_DECOUPL
18 IF_AMP_IN
17 IF_AMP_DECOUPL
16 IF_AMP_OUT
15 GND
14 LIMITER_IN
13 LIMITER_DECOUPL
12 LIMITER_DECOUPL
11 LIMITER_OUT
002aag115
SA676DK/01
QUADRATURE_IN 10
Fig 2.
Pin configuration for SSOP20
6.2 Pin description
Table 2.
Symbol
RF_IN
RF_IN_DECOUPL
OSC_OUT
OSC_IN
RSSI_OUT
V
CC
AUDIO_FEEDBACK
AUDIO_OUT
RSSI_FEEDBACK
QUADRATURE_IN
LIMITER_OUT
LIMITER_DECOUPL
LIMITER_DECOUPL
LIMITER_IN
GND
IF_AMP_OUT
IF_AMP_DECOUPL
IF_AMP_IN
IF_AMP_DECOUPL
MIXER_OUT
Pin description
Pin
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Description
RF input
RF input decoupling pin
oscillator output
oscillator input
RSSI output
positive supply voltage
audio amplifier negative feedback terminal
audio amplifier output
RSSI amplifier negative feedback terminal
quadrature detector input terminal
limiter amplifier output
limiter amplifier decoupling pin
limiter amplifier decoupling pin
limiter amplifier input
ground; negative supply
IF amplifier output
IF amplifier decoupling pin
IF amplifier input
IF amplifier decoupling pin
mixer output
SA676
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 3 — 19 July 2012
3 of 22
NXP Semiconductors
SA676
Low-voltage mixer FM IF system
7. Functional description
The SA676 is an IF signal processing system suitable for second IF systems with input
frequency as high as 100 MHz. The bandwidth of the IF amplifier and limiter is at least
2 MHz with 90 dB of gain. The gain/bandwidth distribution is optimized for 455 kHz,
1.5 k source applications. The overall system is well-suited to battery operation as well
as high performance 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 7.0 dB, conversion gain of 17 dB, and input third-order intercept of
10
dBm. The oscillator will operate in excess of 100 MHz in L/C tank configurations.
Hartley or Colpitts circuits can be used up to 100 MHz for crystal configurations.
The output impedance of the mixer is a 1.5 k resistor permitting direct connection to a
455 kHz ceramic filter. The input resistance of the limiting IF amplifiers is also 1.5 k. With
most 455 kHz ceramic filters and many crystal filters, no impedance matching network is
necessary. The IF amplifier has 44 dB of gain and 5.5 MHz bandwidth. The IF limiter has
58 dB of gain and 4.5 MHz bandwidth.
To achieve optimum linearity of the log signal strength indicator, there must be a 12 dBV
insertion loss between the first and second IF stages. If the IF filter or interstage network
does not cause 12 dBV 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
(IF_AMP_OUT) and the interstage network. The overall gain will then be 90 dB with
2 MHz 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 second-order
temperature compensation if needed. It can drive an AC load as low as 10 k with a
rail-to-rail output.
A log signal strength indicator completes the circuitry. The output range is greater than
70 dB 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 second-order
temperature compensation of the RSSI, if needed.
Remark:
dBV = 20log V
O
/V
I
.
SA676
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 3 — 19 July 2012
4 of 22
NXP Semiconductors
SA676
Low-voltage mixer FM IF system
8. Limiting values
Table 3.
Limiting values
In accordance with the Absolute Maximum Rating System (IEC 60134).
Symbol
V
CC
T
stg
T
amb
Parameter
supply voltage
storage temperature
ambient temperature
operating
Conditions
Min
-
65
40
Max
7
+150
+85
Unit
V
C
C
9. Thermal characteristics
Table 4.
Symbol
Z
th(j-a)
Thermal characteristics
Parameter
transient thermal impedance
from junction to ambient
Conditions
SA676DK/01 (SSOP20)
Max
117
Unit
K/W
10. Static characteristics
Table 5.
Static characteristics
V
CC
= 3 V; T
amb
= 25
C; unless specified otherwise.
Symbol
V
CC
I
CC
Parameter
supply voltage
supply current
Conditions
Min
2.7
-
Typ
-
3.5
Max
7.0
5.0
Unit
V
mA
SA676
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 3 — 19 July 2012
5 of 22
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