Philips Semiconductors
Preliminary specification
IS-54 IF receiver
SA638
PIN DESCRIPTIONS
Pin
No.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
Mnemonic
RF
IN(+)
RF
IN(–)
OSC
B
OSC
E
V
CC1
RSSI/AGC
PWRDWN
OSC
DEMOD
ModeSW
AUDIO/LPF
DEMOD1
Q
I
V
CC2
IQ
REF
GND2
DEMOD2/Offsets
IQ DEMOD
GND1
IFAMP
OUT
V
CCMID
IFAMP
IN
IFAMP
DC
MIX
OUT
RF Input Plus:
Differential RF Plus input to mixer.
RF Input Minus:
Differential RF Minus input to mixer.
LO Oscillator Transistor Base:
LO generator (Pins 3 and 4) with internal buffer to drive mixer differentially. Can
also be driven externally.
LO Oscillator Transistor Emitter:
Pins 3 and 4 are used to form an oscillator with external components (tank,
varactor, etc.).
Supply Voltage 1:
Voltage supply for mixer and main bias.
RSSI Out and AGC Input:
Dual use: RSSI output in AMPS mode (no internal opamp) and AGC input in QPSK
mode if needed. If no AGC, input will auto AGC to pre-defined fixed level for IQ outputs, in which case this pin
also serves as RSSI output.
Power-Down:
Chip power-down input (CMOS compatible).
IF Oscillator Input (LO frequency x4):
Oscillator input x4 for I/Q demodulation is needed for internally
generating quad LOs by division.
Mode Switch:
Logic control signal to select between AMPS and QPSK modes of operation.
Audio Out and LPF Corner Frequency Control:
Dual Use: Audio output in the AMPS mode and LPF corner
frequency control in QPSK mode.
Demod Auxiliary Pin:
Used to implement FM demodulation in AMPS mode.
Baseband Q Ouptut:
Quadrature baseband output referenced to IQ
REF
.
Baseband I Output:
In-phase baseband output referenced to IQ
REF
.
Supply Voltage 2:
Voltage supply for IF amp and demodulator.
I/Q Reference Voltage:
Reference voltage for baseband I/Q outputs.
Ground 2:
Ground common for IF amp and demodulator.
Demod Auxiliary Pin and I/Q Offset Control:
Dual Use: In AMPS mode serves for FM demodulator; in QPSK
mode serves as I/Q offset control.
Input to the Demodulator:
IF input to demodulator from AGC IF amp output.
Ground 1:
Ground common for mixer and main bias.
IF Amplifier Output:
IF amplifier output.
V
CC
Midpoint Bypass:
The internally generated VCC midpoint bias needs to be externally bypassed with a
suitable capacitor.
Input to IF Amplifier:
Input to IF Amplifier from mixer through external filter.
Reference Input to IF Amp:
External bypassing for low frequency feedback of IF amp to null DC offsets.
Output from Mixer:
IF output from mixer to external BPF and IF amp.
Function
ABSOLUTE MAXIMUM RATINGS
SYMBOL
V
CC
V
IN
T
STG
T
A
Single supply voltage
Voltage applied to any other pin
Storage temperature range
Operating ambient temperature range SA639
PARAMETER
RATING
UNITS
V
V
°
C
°
C
NOTE:
θ
JA
Thermal impedance (DH package) 117
°
C/W
1995 Feb 16
2
Philips Semiconductors
Preliminary specification
IS-54 IF receiver
SA638
DC ELECTRICAL CHARACTERISTICS
V
CC
= +3V, T
A
= 25
°
C; unless otherwise stated.
LIMITS
SYMBOL
V
CC
I
CC
Mixer
Conversion power gain
Noise figure
IIP3
Input IP3
Input P-1, input compression
point
Input impedance
IF output impedance
Input frequency range
LO and 2xLO suppression at IF
output
IF frequency
IF Amp, FM Demodulator, RSSI in FM Mode
IF amp gain
Input impedance
Output impedance
RSSI dynamic range
RSSI linearity
Audio output impedance
Audio output level
Audio SINAD for RF signal
-50dBm
Noise figure
Output IP3
IF Amp, AGC, RSSI and IQ Demodulator, QPSK Mode
Input impedance
Gain
Input IP3
RSSI dynamic range
RSSI linearity
LPF frequency control
Channel matching: gain
phase
I/Q output level
I/Q output reference level
NOTE:
1.
for a given tbd linearity; about IQ
output reference level
-2.5
40
1
5
250
tbd
10
tbd
90
+2.5
80
dB
dB
kHz
dB
deg.
mV
PEAK
1.5
95
kΩ
dB
-1.5
300
110
35
11
tbd
dB
90
1.5
150
90
+1.5
dB
kΩ
Ω
dB
dB
Ω
mV
RMS
1kΩ series with 2.5pF
1.5
150
-30
2
kΩ
MHz
dBc
MHz
Input matched externally to tbdΩ,
Output is doubly terminated filter,
1.5kΩ impedance
Single side band
15
8.5
-10
-20
dB
dB
dBm
dBm
PARAMETER
Power supply voltage range
DC current drain
TEST CONDITIONS
MIN
2.7
10
SA639
TYP
MAX
5.5
V
mA
UNITS
1995 Feb 16
3
Philips Semiconductors
Preliminary specification
IS-54 IF receiver
SA638
CIRCUIT DESCRIPTION
The Mixer
The mixer section converts signals up to 150MHz to a 2nd IF of up
to 2MHz (typically around 455KHz) with a power gain of 15dB, input
IP3 of –10dBm and NF of 8.5dB. This section is comnlon to both
modes of operation. An on–chip oscillator is provided (for use with
an external tank, varactor, and synthesizer). The LO section has a
buffer to drive the mixer differentially.
After external bandpass filtering, the signals enter the chip again into
the IF amplifier section. One input of the IF amp is biased to V
ccmid
(which is Vcc/2 generated internally and by–passed externally) and
AC-coupled to the input signal externally while the other IF amp
input is fed back from the amplifier output and AC by–passed to
ground externally. This minimizes low frequency offsets since the
amp is DC-coupled with very high gain.
(Note that, compared to our standard 6xx IF chips, we are freeing
quite a few pins by using only 1 decoupling pin and by NOT splitting
up the IF amp into 2 parts and going in and out for filtering in
between.
In the AMPS mode the amplifier acts as a classic limiter with a fairly
constant output voltage for a very large input voltage range. The
RSSI (Received Signal Strength Indicator) is a temperature
compensated high impedance output signal which acts as a voltage
proportional to Logarithm of the input power and has a 90dB
dynamic range. In the Digital mode the IF amp acts as a linear AGC
(Automatic Gain Controlled) amplifier with maximum gain of 95dB
and an AGC range of 85dB. The control for the AGC can be derived
internally or supplied externally. If not supplied externally the
internal AGC detector will regulate the gain to set the IQ baseband
outputs to a pre–determined level (e.g., 250mV
PEAK
). The RSSI
output which is high impedance will then be available at Pin 6 after
external filtering. On the other hand an external AGC input can
force the voltage at this pin to regulate the gain externally based on
external measurement of say the IQ baseband output voltages. In
such a case the RSSI function is NOT provided by this pin. (This
has been done mainly to conserve pins. Depending on customer
feedback we can provide for separate RSSI output and AGC input
pins if necessary.)
externally as a x4 of the required correct LO signal such that the
internal divider can generate quadrature LO signals of the correct
frequency. After conversion to baseband the signals are filtered for
suppressing LO and its by–products. (We have to decide if this filter
will also provide for accurate baseband filtering. For example TI’s
ARCTIC baseband processor chip provides for such filtering in
which case we do not have to provide for it.) After buffering, the
single ended baseband IQ outputs are available for processing
externally. The signals are referenced to a fixed DC level generated
internally and available througn Pin 15. We can save a pin if the
V
ccmid
(Pin 21) can be used for this purpose. Single-ended outputs
as described above are used rather than differential outputs in order
to save pins.
The FM Demodulator section
The FM Demodulator section will incorporate a new technique wnich
will not require a quad tank. However, a backup technique of the
quad discriminator will be available if the new riskier approach fails.
Because of this, two pins have been allocated for the FM
demodulator in addition to the audio output (similar to our existing
FM–IF products).
In this pinout there is provision for 2 V
CC
pins and 2 ground pins in
addition to a V
CC
/2 bypass pin. This seems necessary in light of the
hign gain values involved in the IF amp block.
There are at least three pins which have dual functionality:
RSSI/AGC; Audio/LPF; Demod2/ IQ Offsets. We have to carefully
look at this to see if this is feasible. If not, the pinout has to be
changed appropriately.
Fallback Positions:
1. We have a fallback for the FM demodulator, the classic FM
discriminator.
2. If the “one IF amp will work for both modes’’ approach fails, we
can provide 2 separate IF amp paths and switch between them
for the different modes. The penalty is increased chip area.
3. The proposed solution for the lF amp is to have all its gain in one
section with no external filtering in between. This is aggressive
since our existing chips have 2 IF sections with separate DC
feedback for each section and external filtering in between. If the
proposed 1 section solution fails, going back to our old technique
will require more pins than we perhaps have!
The IQ Demodulator Section
The IQ Demodulator section takes the signal after external filtering
fronl the chip’s IF anlp output. The I/Q LO is supplied to the chip
1995 Feb 16
4
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