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GP2015
2
FRONT
END
MIXER
VCO
PLL
LOOP
FILTER
EXTERNAL
LOOP
FILTER
2nd
STAGE
MIXER
175.42MHz FILTER
AGC
3rd
STAGE
MIXER
4.3MHz
FILTER
35.42MHz FILTER
÷5
31.11MHz
140MHz
PHASE
DETECTOR
VOLTAGE
REGULATOR
1.400GHz
PHASE-
LOCKED
LOOP
PLL REF I/P
10MHz (REF 2)
40MHz CLOCK O/P
(FOR CORRELATOR
CHIP)
(OPCIK +/-)
PLL LOCK
LOGIC O/P
(LD)
1. 400GHz
(TEST)
AGC
CONTROL
+Vr
-Vr
SIGN
O/P
LATCH
MAG
O/P
LATCH
SIGN
TTL O/P
MAG
TTL O/P
SAMPLE
CLOCK I/P (CLK)
(5.71MHz TTL)
IF Output
(4.309MHz)
A -> D
CONVERTER
RF Input
L1
(1575.42MHz)
PLL
REFERENCE
OSCILLATOR
AGC CAPACITOR
REF 1 I/P
(FOR USE WITH
CRYSTAL REF
ONLY)
+1.21V
POWER-ON
REFERENCE
I/P
(PREF)
POWER-ON
RESET O/P
(PRESET)
POWER
CONTROL
POWER
DOWN I/P
(PDn)
POWER-ON
RESET
(1)
(15)
(14)
(11)
(9)
(19)
(8)
(20)
(28)
(16,17)
(27)
(21)
(3)
(2)
(32)
(37,38)
(40,41)
(44,45)
(47,48)
(23)
(24)
_
+
÷2
÷7
÷4
÷9
ABSOLUTE MAXIMUM RATINGS
(Non-simultaneous)
Max. Supply Voltage
7V
Max. RF Input
+15dBm
Max. voltage on any pin
V
CC/VDD + 0.5V
except LD (pin 21) and PReset (pin 9), which are 5.5V
Min. voltage on any pin
V
EE - 0.5V
Storage Temperature
-65
°C to +150°C
Operation Junction Temperature
-40
°C to +150°C
10MHz Reference Input
1.5V pk -pk
IF STRIP
The input signal to the GP2015 is the GPS L1 signal
received via an antenna and a suitable LNA. The L1 input is
a spread spectrum signal at 1575.42MHz with 1.023Mbps
BPSK modulation. The signal level at the antenna is about
-130dBm, spread over a 2.046MHz bandwidth, so the wanted
signal is actually buried in noise. The high RF input compression
point of the GP2015 means that with subsequent IF filtering
it is possible to reject large out of band jamming signals, in
particular 900MHz as used by mobile telephones.The on-chip
PLL generates the first local-oscillator frequency at 1400MHz.
The output of the front-end mixer (Stage 1) at 175.42 MHz can
then be filtered before being applied to the second stage. The
double-balanced stage 1 mixer outputs are open-collectors,
and require external dc bias to VCC.
The second stage contains further gain and a mixer
with a local oscillator signal at 140 MHz giving a second IF at
35.42 MHz. The second stage mixer is also double-balanced
with open-collector outputs requiring external dc bias to VCC.
The signal from stage 2 is passed through an external
filter with a 1dB bandwidth of 1.9MHz. The performance of this
filter is critical to system performance and it is recommended
that a SAW filter is used (part number DW9255, also available
from Mitel Semiconductor). The output of the filter then feeds
the main IF amplifier. This includes 2 AGC amplifiers and a
third mixer with a local oscillator signal at 31.111 MHz giving
a final IF at 4.309 MHz. There is an on-chip filter after the third
mixer which provides filtering centred on 4.309 MHz. The IF
output, which has 1k
output impedance, is provided for test
purposes. All of the signals within the IF amplifier are differential
including the filter inputs and outputs, except the IF output (pin
1), to reduce any common mode interference.
Fig. 2 Block diagram of GP2015
ESD PROTECTION
The GP2015 device is static sensitive.
The most
sensitive pins withstand a 750V test by the human body
model. Therefore, ESD handling precautions are essential to
avoid degradation of performance or permanent damage to
this device.
PRODUCT DESCRIPTION
The GP2015 receives the 1575.42MHz signal
transmitted by GPS satellites and converts it to a 4.309MHz
IF, using triple down-conversion. The 4.309MHz IF is sampled
to produce a 2-bit digital output. If the GP2015 is used in
conjunction with the GP2021 correlator, then the GP2021
provides a sampling clock of 5.714MHz. This converts the IF
to a 1.405MHz 2-bit digital output at TTL levels.
The GP2015 can operate from a single supply from
+3V (nominal) to +5V (nominal).
A block diagram of the circuit is shown in figure 2.