Philips Semiconductors
Application note
Evaluation of the SA601/SA606 demoboard
Author: Randall Yogi
INTRODUCTION
Philips Semiconductors is dedicated to playing a major role in the
wireless communication market. Key to this goal is Philips’
commitment for design assistance at all levels. This is the purpose
of the SA601/SA606 combo-board. The SA601 is a combined RF
amplifier and mixer designed for high-performance low-power
communication systems from 800-1200MHz. The SA606 is a
low-voltage high performance monolithic FM IF system that, when
combined with the SA601, results in a high performance double
down-conversion FM receiver. To better support this type of
application, Philips has combined the SA601 and SA606 ICs onto a
single board which highlights how well the SA601 and the SA606
work together. This application note explains how to overcome
many of the technical problems that might arise, and shows how to
achieve the best possible performance from the SA601 and SA606.
Test results are also included.
This application note is divided into four main sections:
I. Overview of the SA601/SA606 combination board
II. Layout
A. Schematic, Components Specifics and Parts List
B. Impedance Matching
III. Performance
A. Test Setup and Procedures
B. Test Data and Results
IV. Conclusion
A. Q/A section
AN1000
demoboards were cascaded together, along with an RF SAW filter
and a 1st IF SAW filter. The performance with this configuration was
satisfactory, thus permitting the next step of combining everything on
one board (Figure 2). As with the original SA601 and SA606
individual demoboards, the majority of the components are on one
side of the board.
The SA601/SA606 demoboard layout can be configured to provide
two different types of matching to the IF SAW filter (Figure 1). It can
be configured as a 50
Ω
impedance match, or a high impedance
match to the 83.161MHz SAW filter. The 50
Ω
impedance matching
network allows a designer to evaluate or troubleshoot each
individual block. For example, a designer can find conversion gain
measurements of the SA601 or measure SINAD for only the SA606
block.
SA601
MATCHING
NETWORK
50Ω
or
HIGH IMPEDANCE
MURATA
83.161MHz
SAW FILTER
MATCHING
NETWORK
50Ω
or
HIGH IMPEDANCE
SA606
SR00785
Figure 1. Block Diagram: Matching 1st IF SAW Filter
I. OVERVIEW
Both the SA601 and the SA606 are designed for portable, low
voltage, low power communication applications. For a better
understanding of what is involved in combining these boards, or for
more information regarding the individual boards, please review
application notes AN1777 (for the SA601) and AN1993-AN1996 (for
the Second-IF ICs) which can be found in the Philips RF/Wireless
Communications Data Handbook, IC17.
The SA601/SA606 demoboard is designed to meet AMPS
specifications. Section 2 of the EIA Interim Standard,
“Recommended Minimum Standard for 800MHz Cellular Subscriber
Units” (EIA/IS-19-B), was consulted as a guide. Specific sections
used were:
2.3.1 RF Sensitivity
2.3.2 Adjacent and Alternate Channel Desensitization
2.3.3 Intermodulation Spurious-Response Interference
2.3.4 Protection Against Spurious Response
Measured results demonstrate that the SA601/SA606 demoboard
successfully meets and surpasses the specifications listed above.
Although the SA601/SA606 demoboard is designed to meet AMPS
cellular specifications, it can be modified for other analog cellular
specifications such as TACS, ETACS, and NAMPS. The
demoboard could also be configured for ISM band (902MHz –
928MHz) applications.
The 50
Ω
impedance match can also be used as a reference for the
high impedance match. Because 50
Ω
impedance matching
requires more components, a high impedance match is preferred.
Matching for high impedance can be difficult, but since each block is
optimized through a 50
Ω
impedance match, the designer has a
target/reference. For example, if 12dB SINAD = -120dBm for a 50
Ω
impedance matched system, ideally a high impedance match should
yield the same results, if not better.
The majority of the single-board layout was adapted from the
individual application demoboards, except for the two SAW filters
(the image rejection filter centered at 881MHz and the 83.161MHz
SAW filter). The layout for the two filters required additional design
work. The 881MHz image-rejection SAW filter was placed between
the LNA-Out and the Mixer-In of the SA601. Placement of the
881MHz image reject SAW filter, whether it was on the top or bottom
of the board, did not have a dramatic impact on performance. This
was because isolation between the LNA-Out and the Mixer-In trace
had already been considered in the SA601 demoboard. However,
because of its high Q, narrowband, and high impedance, the
83.161MHz SAW filter was much more difficult to position. Its
placement was critical in passing AMPS specification 2.3.4
Protection Against Spurious-Response Interference. The
specification was met with margin to spare by moving the Mixer-Out
(Pins 13 and 14) of the SA601 as far away as possible from RF-In
(Pin 1) of the SA606.
Schematic, Components Specifics, and Parts List
The schematic shown in Figure 3 is for both 50
Ω
impedance
matching and high impedance matching to the 83.161MHz SAW
filter. The schematic shows the configuration for 50
Ω
impedance
matching. By making the modifications listed in the box on the
bottom right of the schematic (Figure 3), the board can be
configured for a high impedance match.
Table 1 lists the basic function of each external component for the
schematic shown in Figure 3. This may help answer any questions
that arise about the specifics of the board.
4–2
II. LAYOUT
The layout of any high frequency board is critical and always
challenging. As stated previously, understanding each board
separately is the key to combining them. Before a single-board
layout was attempted, the SA601 and the SA606 individual
1997 Aug 20
Philips Semiconductors
Application note
Evaluation of the SA601/SA606 demoboard
AN1000
Table 1. Components List: Description of Functionality
Part #
C1
C2
C3
C4
C5, C9, C14, C15, C24, C25
C6, C8, L3
C7, L2
C10, C13
C11
C12
C16, C17, L4, L5
C18, C19, L6
C20
C21, C22, C23, L7, L8
C26, C34
C27
C28, R5, R6
C29, L9
C30
C31
C32, C33
C35, C36
R1
R2
R3
R4
R7
R8, R9
L1
LNA Mixer input DC blocking cap
Part of the matching network that optimizes the return loss while minimizing the degradation of the noise figure
Voltage compensation cap for the LNA
LO DC blocking cap
Supply bypassing
Part of the differential to single-ended translation circuit of the mixer out
Part of the matching network of the mixer output
Part of the matching network that optimizes the return loss while minimizing the degradation of the noise figure
Mixer Input DC blocking cap
LNA Output DC blocking cap
Part of the matching network of the 83.161MHz SAW filter
Part of the tapped-C network that matches the RF input of the SA606
AC grounds Pin 2, the RF input of the SA606
Colpitts oscillator network
AC de-coupling cap
DC blocking cap
Part of the filter network that filters 3kHz-15kHz on the SA7025 (Low-voltage 1GHz fractional-N synthesizer).
This network is only used on the 7025 IC production tester.
Quad tank component that resonates at 455kHz
AC grounds the quad tank
Provides the 90° phase shift to the phase detector
IF limiter decoupling cap
IF amp decoupling cap
DC pull-up resistor that provides isolation (reduces IF to LO and RF to LO leakage)
Sets output impedance of the Mixer Output
Part of the Audio op-amp that sets a gain of 2dB thus stabilizing distortion
Part of the Audio op-amp that sets a gain of 2dB thus stabilizing distortion
Lowers the Q of the quad tank and thus lowers the S-Curve slope
Part of a network to control linearity of the RSSI
Voltage compensation to LNA
Murata SAFC881.5MA70N-TC 881.5MHz bandpass SAW filter: This is a 869MHz to 894MHz bandpass filter. It
is used to reject the image frequency (LO + 83.16MHz in our case) and to attenuate the transmit signal
(RF-45MHz) leaking through the duplexer so that the SA601 mixer doesn’t reach its 1dB compression point from
a strong signal leaking through. Some electrical characteristics from Murata are provided (Table 2).
Murata SAFC83.161MA51X-TC 83.161MHz SAW filter: 1st-IF filter for attenuating adjacent and alternate
channel spurs. The filter plays a larger role in achieving the high performance of the receiver in areas such as
dynamic range, spurious performance, and data communication accuracy. The 83.16MHz SAW filter provides a
30kHz bandpass characteristic utilizing electrodes deposited on a piezoelectric substrate. These electrodes
form an inter-digitated pattern on the substrate and serve as transducers to launch an acoustic wave. When an
RF voltage is applied to one set of transducers, an electric field is generated and causes the acoustic waves to
propagate along the surface to an opposite transducer where an output voltage is produced. (See Reference 8,
Alan Victor). The Electrical Characteristics for the Murata SAW filter are shown in Table 3.
Murata SFGCG455BX-TC 455kHz bandpass filter (30kHz bandwidth).
An 82.705MHz crystal from either HY-Q or Reeves Hoffman is a 3rd overtone crystal used to generate the LO for
the SA606
Description
FILT1
FILT2
FILT3, 4
X1
1997 Aug 20
4–5
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