GP2015

2

FRONT

END

MIXER

VCO

PLL

LOOP

FILTER

EXTERNAL

LOOP

FILTER

2nd

STAGE

MIXER

175.42MHz FILTER

AGC

AGC

3rd

STAGE

MIXER

4.3MHz

FILTER

35.42MHz FILTER

÷5

÷5

÷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

except LD (pin 21) and PReset (pin 9), which are 5.5V

Min. voltage on any pin

V

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,

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

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

Ω 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.