SA58641
High performance mixer FM IF system with high-speed RSSI
Rev. 2 — 9 March 2012
Product data sheet
1. General description
The SA58641 is a high performance monolithic FM IF system with high-speed RSSI
incorporating a mixer/oscillator, two limiting intermediate frequency amplifiers, quadrature
detector, logarithmic Received Signal Strength Indicator (RSSI), voltage regulator,
wideband data output and fast RSSI op amps. The SA58641 is available in 20-lead SSOP
(Shrink Small Outline Package).
The SA58641 was designed for high bandwidth portable communication applications and
will function down to 3 V. The RF section is similar to the famous SA605. The data output
has a minimum bandwidth of 600 kHz. This is designed to demodulate wideband data.
The RSSI output is amplified. The RSSI output has access to the feedback pin. This
enables the designer to adjust the level of the outputs or add filtering.
SA58641 incorporates a power-down mode which powers down the device when pin 8
(POWER_DOWN_CTRL) is LOW. Power-down logic levels are CMOS and TTL
compatible with high input impedance.
2. Features and benefits
Wideband data output (600 kHz minimum)
Fast RSSI rise and fall times
Low power consumption: 7.5 mA typical at 5 V
Mixer input to >500 MHz
Mixer noise figure of 12 dB at 240 MHz
Crystal oscillator effective to 150 MHz (LC oscillator to 1 GHz local oscillator can be
injected)
92 dB of IF amp/limiter gain
25 MHz limiter small signal bandwidth
Temperature compensated logarithmic RSSI with a dynamic range in excess of 90 dB
RSSI output internal op amp
Internal op amps with rail-to-rail outputs
Low external component count; suitable for crystal/ceramic/LC filters
Excellent sensitivity: 0.54
V
into 50
matching network for 12 dB SINAD
(Signal-to-Noise-And-Distortion ratio) for 1 kHz tone with RF at 240 MHz and IF at
10.7 MHz
ESD hardened
10.7 MHz filter matching (330
)
Power-down mode (I
CC
= 200
A)
NXP Semiconductors
SA58641
High performance mixer FM IF system with high-speed RSSI
3. Applications
DECT (Digital European Cordless Telephone)
Digital cordless telephones
Digital cellular telephones
Portable high performance communications receivers
Single conversion VHF/UHF receivers
FSK and ASK data receivers
Wireless LANs
4. Ordering information
Table 1.
Ordering information
T
amb
=
40
C to +85
C
Type number
SA58641DK
Topside mark
SA58641
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
IF_AMP_DECOUPL
IF_AMP_DECOUPL
20
19
18
17
16
15
14
13
12
IF amp
mixer
limiter
quad
OSC
FAST
RSSI
POWER
DOWN
7
RSSI_OUT
8
POWER_DOWN_CTRL
1
RF_IN
2
RF_IN_DECOUPL
E
3
OSC_OUT
B
4
OSC_IN
RSSI
audio
5
V
CC
6
RSSI_FEEDBACK
9
DATA_OUT
002aac973
Fig 1.
Block diagram of SA58641
SA58641
All information provided in this document is subject to legal disclaimers.
QUADRATURE_IN
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 2 — 9 March 2012
LIMITER_OUT
11
10
IF_AMP_OUT
MIXER_OUT
LIMITER_IN
IF_AMP_IN
GND
2 of 26
NXP Semiconductors
SA58641
High performance mixer FM IF system with high-speed RSSI
6. Pinning information
6.1 Pinning
RF_IN
RF_IN_DECOUPL
OSC_OUT
OSC_IN
V
CC
RSSI_FEEDBACK
RSSI_OUT
POWER_DOWN_CTRL
DATA_OUT
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
002aac972
SA58641DK
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
V
CC
RSSI_FEEDBACK
RSSI_OUT
POWER_DOWN_CTRL
DATA_OUT
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 (emitter)
oscillator input (base)
positive supply voltage
RSSI amplifier negative feedback terminal
RSSI output
power-down control, active HIGH
data output
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
SA58641
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 2 — 9 March 2012
3 of 26
NXP Semiconductors
SA58641
High performance mixer FM IF system with high-speed RSSI
7. Functional description
The SA58641 is an IF signal processing system suitable for second IF or single
conversion systems with input frequency as high as 1 GHz. The bandwidth of the IF
amplifier is about 40 MHz with 38 dB of gain from a 50
source. The bandwidth of the
limiter is about 28 MHz with about 54 dB of gain from a 50
source. However, the
gain/bandwidth distribution is optimized for 10.7 MHz, 330
source applications. The
overall system is well-suited to battery operation as well as high performance and high
quality products of all types such as cordless and cellular hand-held phones.
The input stage is a Gilbert cell mixer with oscillator. Typical mixer characteristics include
a noise figure of 14 dB, conversion gain of 11 dB, and input third-order intercept of
16
dBm. The oscillator will operate in excess of 1 GHz in L/C tank configurations. Hartley
or Colpitts circuits can be used up to 100 MHz for crystal configurations. Butler oscillators
are recommended for crystal configurations up to 150 MHz.
The output of the mixer is internally loaded with a 330
resistor permitting direct
connection to a 10.7 MHz ceramic filter for narrowband applications. The input resistance
of the limiting IF amplifiers is also 330
.
With most 10.7 MHz ceramic filters and many
crystal filters, no impedance matching network is necessary. For applications requiring
wideband IF filtering, such as DECT, external LC filters are used (see
Figure 16).
To
achieve optimum linearity of the log signal strength indicator, there must be a 6 dBV
insertion loss between the first and second IF stages. If the IF filter or interstage network
does not cause 6 dBV insertion loss, a fixed or variable resistor can be added between
the first IF output (IF_AMP_OUT) and the interstage network.
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.
Overall, the IF section has a gain of 90 dB for operation at intermediate frequency at
10.7 MHz. Special care must be given to layout, termination, and interstage loss to avoid
instability.
The demodulated output (DATA_OUT) of the quadrature is a voltage output. This output is
designed to handle a minimum bandwidth of 600 kHz. This is designed to demodulate
wideband data, such as in DECT applications.
A Received Signal Strength Indicator (RSSI) completes the circuitry. The output range is
greater than 90 dB and is temperature compensated. This log signal strength indicator
exceeds the criteria for AMPS or TACS cellular telephone, DECT and RCR-28 cordless
telephone. 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
.
SA58641
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 2 — 9 March 2012
4 of 26
NXP Semiconductors
SA58641
High performance mixer FM IF system with high-speed RSSI
8. Internal circuitry
Table 3.
Symbol
RF_IN
RF_IN_DECOUPL
Internal circuits for each pin
Pin
1
2
DC Voltage Equivalent circuit
+1.07 V
+1.07 V
0.8 kΩ
0.8 kΩ
1
2
002aac983
OSC_OUT
OSC_IN
3
4
+1.57 V
+2.32 V
18 kΩ
4
MIX
3
002aac984
V
CC
5
+3.00 V
V
REF
5
BANDGAP
002aac985
RSSI_FEEDBACK
6
+0.20 V
V
CC
6
−
+
002aac986
SA58641
All information provided in this document is subject to legal disclaimers.
© NXP B.V. 2012. All rights reserved.
Product data sheet
Rev. 2 — 9 March 2012
5 of 26
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