SL1925 查看數據表（PDF） - Mitel Networks
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SL1925 Datasheet PDF : 20 Pages
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Preliminary Information
Quick Reference Data
Characteristic
Operating range
Input noise figure, DSB, maximum gain, 1500MHz
Maximum conversion gain (assuming 6dB filter loss)
Minimum conversion gain (assuming 6dB filter loss)
IP32T input referred
Converter input referred IM3, two tones at 97dBµV
IP22T input referred
P1dB input referred
Baseband amplifier Output limit voltage
Gain match up to 22 MHz
Phase match up to 22 MHz
Gain flatness up to 22 MHz
Local oscillator phase noise across entire 950MHz to 2150MHz band:
SSB @ 10 kHz offset
Table 1
950-2150
19
>55
<20
113
30
140
103
2.0
0.2
0.7
0.5
80
SL1925
Units
MHz
dB
dB
dB
dBuV
dBc
dBuV
dBuV
V
dB
deg
dB
dBc/Hz
Functional Description
The SL1925 is a wideband direct conversion quadrature
downconverter optimised for application in satellite
receiver systems. A block diagram is given in Figure 2
and shows the device to include a broadband RF
preamplifier with AGC control, two oscillator sustaining
amplifiers, a frequency agile 90° phase splitter, I Q
channel mixers and I Q channel baseband amplifiers.
The only additional elements required are an external
tank circuit for each oscillator, and baseband interstage
filters. To fabricate a complete tuner an RF AGC stage
offering +20dB to -10 dB of gain range and a 2.2 GHz
PLL frequency synthesiser are also required. An example
application is shown in Figure 16.
In normal application the first satellite IF frequency of
typically 950 to 2150 MHz is fed via the tuner RF AGC
stage to the RF preamplifier, which is optimised for
impedance match and signal handling. The RF
preamplifier is designed such that no tracking RF filter is
required and also allows for analog interferers at up to
10 dB higher amplitude. The converter RF input
impedance is shown in Figure 5. The amplifier signal is
then fed to an AGC stage providing a minimum of 35dB
AGC control, which together with the RF attenuator
provides a possible overall tuner dynamic range of
65dB, to allow for normal operating dynamic range and
MCPC systems. The signal is then split into two balanced
channels to drive the I and Q mixers. The AGC
characteristic, and gain variation of IIP3, IIP2, P1dB and
NF are contained in Figs. 6, 7, 8, 9 and 10 respectively.
The required 950MHz to 2150MHz I and Q reference LO
frequencies for quadrature direct conversion are
generated by the on board oscillators named ‘vcos’ and
‘vcov’, and the phase splitter. Oscillator ‘vcos’ operates
nominally from 1900MHz to 3000MHz and is then divided
by two to provide 950MHz to 1500MHz. Oscillator ‘vcov’
operates nominally from 1400MHz to 2150MHz. Only
one oscillator is active at any time and selection is made
within the phase splitter under the control of the LOsel
input. Each oscillator uses an external varactor tuned
resonant network optimised for low phase noise with a
single varactor line control. A recommended application
circuit for the oscillators is shown in Figure 4. The LO
from the phase splitter drives a buffer whose outputs
‘PSout’ and ‘PSoutb’ can be used for driving an external
PLL control loop for the VCO’s. The typical LO phase
noise is shown in Figure 11.
The mixer outputs are coupled to baseband buffer
outputs ‘OPFI’ and ‘OPFQ’ which drive external band
limit filters. The output impedance of these buffers is
contained in Figure 12. The outputs of the filters are then
connected to the inputs ‘IPFI’ and ‘IPFQ’ of the baseband
channel amplifiers. The outputs ‘Iout’ and ‘Qout’ provide
for a low impedance drive and can be used with a
maximum load as in Figure 3. The output impedance of
this section is contained in Figure 13. An example filter
for application with 30MS/s systems is contained in
Figure 14.
All port peripheral circuitry for the SL1925 is shown in
Figure 15a and 15b.
The typical key performance data at 5V Vcc and 25°C
ambient are shown in the ‘QUICK REFERENCE DATA’
of Table 1.
3
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