uaa1570hl NXP Semiconductors, uaa1570hl Datasheet - Page 35

• Manufacturer Part Number: uaa1570hl
• Description: Global Positioning System Gps Front-end Receiver Circuit
• Manufacturer: NXP Semiconductors

Philips Semiconductors
7.8.1
Both the reference and the sample clock input can be
driven by a Temperature Compensated Crystal Oscillator
(TCXO). Typical TCXOs produce 0.5 to 1.0 V (p-p) clipped
sine wave outputs. The drive capability is typically 20 k in
noise crystal reference source should be AC-coupled to
this port. Reference inputs up to 35 MHz and levels
between 50 to 500 mV (peak value) are acceptable. This
source can be externally squared and attenuated before
1999 May 10
parallel with 5 pF or 10 k in parallel with 10 pF. Some
TCXOs are even capable of driving loads as low as 1 k
without buffering.
Alternatively, cost can be reduced by designing a simple
discrete crystal oscillator reference, paying careful
attention to temperature tolerance ( 6 ppm) as well as
shock and vibration characteristics.
Both UAA1570HL clock inputs, the synthesizer reference
input REFIN (pin 8), and the sample clock input SCLK
(pin 37), accept low level inputs and provide internal
gain/squaring circuits.
The reference clock input has a high impedance with
20 k in parallel with 0.07 pF. A high stability, low phase
handbook, full pagewidth
Global Positioning System (GPS) front-end
receiver circuit
(1) T
(2) T
(3) T
R i(diff)
(k )
amb
amb
amb
C
8
6
4
2
0
10
LOCK INPUTS
= 55 C.
= +27 C.
= +120 C.
2
Fig.24 Limiter differential input resistance as a function of frequency (simulated).
10
1
1
(3)
(2)
(1)
35
10
being applied. Direct sinusoidal inputs should be as large
as possible within the prescribed range to optimize phase
noise performance.
The sample clock input also features a high impedance of
23.3 k . The sample clock input can be AC-coupled
directly to the reference if the system sampling objectives
are met. Alternatively, the TCXO/XO reference can be
externally squared to CMOS input levels and applied to the
SAA1575HL RCLK input (pin 98) and divided under
firmware control to produce a signal commensurate with
the sampling objective.
Due to the wide range of programmable frequency plans
and sampling rates supported by the UAA1570HL, it is not
possible to predict the frequencies and levels of the
associated spurious products that will be generated.
One significant source of potential spurs are the
harmonics of the reference and sampling signals. The
availability of on-chip squaring circuits provide some
freedom to minimize large digital signal effects in sensitive
RF circuit areas. In most cases digital sampling signal
levels are acceptable as long as careful attention is paid to
avoid injecting these signals or their harmonics into the
pass bands of the IF filters.
10
2
10
3
UAA1570HL
Product specification
f (MHz)
MHB287
10
4