RF250
Rx ASIC for CDMA, AMPS, and PCS Applications
The RF250 Application-Specific Integrated Circuit (ASIC) is a
triple-mode, dual-band receiver (Rx) intended for use in Code
Division Multiple Access (CDMA) portable phones in both
cellular and Personal Communications System (PCS) bands. As
a dual mode IC, it can be used in CDMA mode or Advanced
Mobile Phone System (AMPS) mode.
The device incorporates all the components required to
implement the receiver front end and the In-Phase and
Quadrature (I/Q) demodulator stages except for the filter blocks
and PCS Low Noise Amplifier (LNA). Besides a cellular band
LNA, there are separate mixers for AMPS, CDMA 800 MHz, and
PCS bands. The AMPS mixer output is single-ended, followed
by the AMPS Intermediate Frequency (IF) Surface Acoustic
Wave (SAW) filter. The cellular and PCS mixers have balanced
outputs for the CDMA IF SAW filters. The mixers are followed by
an IF Variable Gain Amplifier (VGA) and an I/Q demodulator.
The outputs from the filters are combined through separate
buffers at the input of the VGA. The buffers are enabled
depending on the selected mode. The VGA has a gain control
range greater than 90 dB. There are two VHF oscillators that
operate with external tank circuits. They provide signals to the
Local Oscillator (LO) for the I/Q demodulator in the cellular and
PCS bands.
The noise figure, gain, and third order Input Intercept
Point (IIP3) of each stage in the receiver chip are
optimized to meet the system requirements for AMPS
and CDMA modes as per TIA/EIA-98-B and ANSI J-
STD-018 (PCS). Employing silicon bipolar technology,
the ASIC is designed for high performance and a high
level of integration.
GND
1
2
3
4
5
6
7
8
9
10
11
Features
•
•
•
•
•
•
•
Supports CDMA/AMPS/PCS1900
modes.
Three battery cell operation
(2.7 V < VCC < 3.6 V).
Higher level of integration.
I/Q outputs.
On-chip 100 to 640 MHz oscillators.
Low power operation: <60 mA.
48-pin Thin Quad Flat Pack (TQFP)
package with downset paddle.
Applications
•
•
Tri-mode handsets.
CDMA and AMPS modes in the
cellular band:
- AMPS
- CDMA-US
- CDMA-J
CDMA mode in the PCS band:
- US-PCS
•
- K-PCS
48 47 46 45 44 43 42 41 40 39 38 37
36
35
34
33
32
31
30
29
28
27
26
PCS_MIX_BYPASS
CELL_LNA_OUT
CELL_MIX_GND
PCS_BIAS_SET
CELL_IFTRAP
CELL_MIX_IN
PCS_MIX_IN
CELL_LO
PCS_LO
VCC4
GND
NC
PCS_IF_OUT+
PCS_IF_OUT-
AMPS_IF_OUT
CDMA_IF_OUT+
CDMA_IF_OUT-
CELL_MIX_BYPASS
VGA_PCS_IN+
VGA_PCS_IN-
VGA_AMPS_IN
VGA_CDMA_IN+
VGA_CDMA_IN-
VCC3
The device package and pinout are shown in Figure 1. A
block diagram of the RF250 is shown in Figure 2.
CELL_LNA_DECOUPLE
NC
CELL_LNA_IN
VCC1
CELL_BIAS_SET
CELL/PCS
FM/CDMA
VCC2
GND
CELL_TANK-
CELL_TANK+
25
12
13 14 15 16 17 18 19 20 21 22 23 24
PCS_TANK+
DIV2/DIV4
PLL+
PLL-
GND
I-
I+
Q+
Q-
VGA_CONTROL
PCS_TANK-
SLEEP
C452
Figure 1. RF250 Rx ASIC Pinout – 48-Pin TQFP
Package With Downset Paddle
Data Sheet
Conexant Systems, Inc.
Doc. No. 101251A
August 24, 2000
Rx ASIC
RF250
RF SAW(CELL)
AMPS IF SAW
CDMA IF SAW
FM/CDMA
48
42
34
8
28
2
2
2
32, 33
26, 27
11,12
CELL_LNA_IN
4
19
I
20
CELL/PCS
7
RF250
Rx ASIC
23
÷ 2,4
21
SLEEP
Q
22
40
35,36
2
29,30
2
38
39
24
13,14
2
16,17
PCS_LNA_IN
VGA_CONTROL
CELL_LO
PCS_LO
PLL
RF SAW (PCS)
IF SAW (PCS)
C262
Figure 2. RF250 Rx ASIC Block Diagram
Technical Description
Low Noise Amplifier (LNA).
The cellular band
LNA is designed with a low noise figure and high
linearity to achieve maximum receiver dynamic
range. Pin 2, the 800 LNA decouple pin, is
required to be grounded through an RF bypass
capacitor with minimum trace length. The input
and output match are external to the chip.
Mixers.
The RF250 Rx ASIC has three
independent mixers, one for the PCS band and
two for the cellular band (AMPS and CDMA).
The mixers are designed to operate with very low
LO powers of –10 dBm. The LO ports are matched
internal to the chip.
The cellular band mixers have a high gain and a
low noise figure that allow them to meet the
system noise figure. The cellular CDMA and PCS
mixers have balanced output to drive the IF filters.
The AMPS mixer has a single-ended output to
match the standard IF SAW filters.
Variable Gain Amplifier (VGA).
The high dynamic
range required by CDMA handsets is achieved by
the VGA, which is common to all modes. The VGA
2
has a minimum dynamic range of 90 dB with a
control voltage of 0.2 to 2.7 volts. The appropriate
signal path is switched internal to the device. This
eliminates off-chip switching needed to operate
this common VGA in cellular AMPS, CDMA, and
PCS modes.
I/Q Demodulator.
The local oscillator signals are
generated on-chip. The I/Q demodulator is
internally connected to the VGA output. It is
designed to have a very low amplitude and phase
imbalance. The I and Q outputs are differential.
The DC offsets between the differential outputs
and between I and Q channels are designed to be
extremely low to facilitate compatibility with
baseband Interfaces.
VHF Oscillators.
There are two on-chip
oscillators, one for the cellular and one for the PCS
bands. These Voltage Controlled Oscillators
(VCOs) work with external tank circuits and
varactor diodes. The outputs of the differential
oscillators are buffered and the output is used to
drive the prescaler of an external Phase Locked
Loop (PLL). The VCOs typically operate at twice
the IF frequency and can operate at up to four
times the IF frequency.
101251A
August 24, 2000
Conexant Systems, Inc.
RF250
Rx ASIC
The local oscillators for the I/Q demodulators are
derived by an on-chip frequency divider. The logic
signal to select the divider ratio (2 or 4) is available
on Pin 15 (DIV2/DIV4).
Mode Control.
The operation of the chip is
controlled by signals at Pin 7 (CELL/PCS), Pin 8
(FM/CDMA), Pin 23 (SLEEP), and the DIV2/DIV4
select commands at Pin 15. All the switching is
done internally. The supply voltage should be
present at all the VCC pins for normal operation.
The internal switching needed to select each of
these signals is shown in Table 1.
Electrical and Mechanical Specifications.
Included in this document are Tables 1 through 5
and Figures 1 through 29, which define the
electrical and mechanical specifications of the
RF250.
Table 1:
Table 2:
Table 3:
Table 4:
Table 5:
Figure 1:
Mode Control Select Signal
Switching
Pin Assignments and Functional
Pin Descriptions
Absolute Maximum Ratings
Recommended Operating
Conditions
Electrical Specifications
Pinout Configuration
Figure 2:
Functional Block Diagram
Figures 3 - 27: Typical Functional Block
Performances
Figure 28:
Package Dimensions
Tape and Reel
Figure 29:
Dimensions
ESD Sensitivity
The RF250 is a Class 1 device. The following
extreme Electrostatic Discharge (ESD) precautions
are required according to the Human Body Model
(HBM):
•
•
•
•
Protective outer garments.
Handle device in ESD safeguarded work
area.
Transport device in ESD shielded
containers.
Monitor and test all ESD protection
equipment.
The HBM ESD withstand threshold value, with
respect to ground, is
±1.5
kV. The HBM ESD
withstand threshold value, with respect to VDD
(the positive power supply terminal) is also
±1.5
kV.
Pin
7 (CELL/PCS)
8 (FM/CDMA)
15 (DIV2/DIV4)
23 (SLEEP)
Key: 0 = LOW
1 = HIGH
x = N/A
AMPS
0
0
0
1
CDMA
0
1
0
1
PCS
1
x
0
1
Table 1. Mode Control Select Signal Switching
101251A
August 24, 2000
Conexant Systems, Inc.
3
Rx ASIC
RF250
Table 2. RF250 Signal Description (1 of 2)
Pin #
1
2
3
4
GND
CELL_LNA_DECOUPLE
NC
CELL_LNA_IN
Name
Ground
An RF bypass capacitor with very short trace should be connected to this pin.
No connection
The input to LNA needs external matching. The matching network should be placed as close
to this pin as possible. High Q components are recommended to minimize the effect on the
noise figure.
Supply voltage to the RF bias. An RF bypass capacitor should be connected from the pin to
ground with short traces..
This pin sets the cellular RF bias current. Typically, a 180
Ω
resistor is connected from the
pin to ground.
Band select: 0 = cellular (800 MHz); 1 = PCS (1900 MHz).
Cellular band mode select: 0 = AMPS; 1 = CDMA.
Voltage supply pin to the VCO buffer. A bypass capacitor should be placed close to the
device from pin 9 to pin 10. The trace should be short and connected immediately to the
ground plane for best performance.
Ground return from the VCO buffer.
Differential tank connection for the cellular band VCO. Care should be taken during the
layout of the external tank circuit to prevent parasitic oscillations.
Differential tank connection for the cellular band VCO. Care should be taken during the
layout of the external tank circuit to prevent parasitic oscillations.
Differential tank connection for the PCS band VCO. Care should be taken during the layout
of the external tank circuit to prevent parasitic oscillations.
Differential tank connection for the PCS band VCO. Care should be taken during the layout
of the external tank circuit to prevent parasitic oscillations.
Selects the divide ratio of the VCO to the LO port of the I/Q demodulator: 0 = divide by 2,
1 = divide by 4.
Differential buffered VCO output.
Differential buffered VCO output.
Ground
I channel differential output.
I channel differential output.
Q channel differential output.
Q channel differential output.
Activates sleep mode: 0 = sleep; 1 = enable
VGA voltage input. Input impedance is greater than 50K
Ω.
Voltage supply to VGA and I/Q demodulator stages. Supply should be well regulated and
bypassed to prevent modulation of the signal by the supply ripple.
CDMA differential VGA input
CDMA differential VGA input
AMPS VGA input.
Description
5
6
7
8
9
VCC1
CELL_BIAS_SET
CELL/PCS
FM/CDMA
VCC2
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
GND
CELL_TANK–
CELL_TANK+
PCS_TANK–
PCS_TANK+
DIV2/DIV4
PLL+
PLL–
GND
I–
I+
Q+
Q–
SLEEP
VGA_CONTROL
VCC3
VGA_CDMA_IN–
VGA_CDMA_IN+
VGA_AMPS_IN
4
Conexant Systems, Inc.
101251A
August 24, 2000
RF250
Rx ASIC
Table 2. RF250 Signal Description (2 of 2)
Pin #
29
30
31
32
33
34
35
36
37
38
39
40
41
Name
VGA_PCS_IN–
VGA_PCS_IN+
CELL_MIX_BYPASS
CDMA_IF_OUT–
CDMA_IF_OUT+
AMPS_IF_OUT
PCS_IF_OUT–
PCS_IF_OUT+
PCS_MIX_BYPASS
PCS_LO
CELL_LO
PCS_MIX_IN
VCC4
PCS differential VGA input.
PCS differential VGA input.
Low frequency bypass for the AMPS mixer.
CDMA differential mixer output. Requires an external inductor to VCC. Output impedance is
set by an external match.
CDMA differential mixer output. Requires an external inductor to VCC. Output impedance is
set by an external match.
AMPS mixer output. Requires an external inductor to VCC. Output impedance is set by an
external match.
PCS differential mixer output. Requires an external inductor to VCC. Output impedance is
set by an external match.
PCS differential mixer output. Requires an external inductor to VCC. Output impedance is
set by an external match.
Low frequency bypass for the PCS mixer.
The local oscillator input for the PCS band.
The local oscillator input for the cellular band.
PCS mixer input.
Voltage supply pin for the mixers. An RF bypass capacitor should be connected from this pin
to ground. It should be connected as close to the device as possible with very short trace
lengths.
Cellular mixer input.
The parallel LC circuit is tuned to the cellular IF frequency.
Add inductance from the pin to ground to lower mixer gain and increase IIP3.
No connection
This pin sets the PCS RF bias current. Typically, a 180
Ω
resistor is connected from the pin
to ground.
Ground
Cellular band LNA output. This is an open collector output. An inductor must be connected to
VCC. The matching is done externally to the chip.
Description
42
43
44
45
46
47
48
CELL_MIX_IN
CELL_IFTRAP
CELL_MIX_GND
NC
PCS_BIAS_SET
GND
CELL_LNA_OUT
101251A
August 24, 2000
Conexant Systems, Inc.
5
