MC13150FTA Просмотр технического описания (PDF) - Motorola => Freescale
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MC13150FTA Datasheet PDF : 20 Pages
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MC13150
MC13150 CIRCUIT DESCRIPTION
General
The MC13150 is a very low power single conversion
narrowband FM receiver incorporating a split IF. This device
is designated for use as the backend in analog narrowband
FM systems such as cellular, 900 MHz cordless phones and
narrowband data links with data rates up to 9.6 k baud. It
contains a mixer, oscillator, extended range received signal
strength indicator (RSSI), RSSI buffer, IF amplifier, limiting IF,
a unique coilless quadrature detector and a device enable
function (see Package Pin Outs/Block Diagram).
Low Current Operation
The MC13150 is designed for battery and portable
applications. Supply current is typically 1.7 mAdc at 3.0 Vdc.
Figure 2 shows the supply current versus supply voltage.
Enable
The enable function is provided for battery powered
operation. The enabled pin is pulled down to enable the
regulators. Figure 3 shows the supply current versus enable
voltage, Venable (relative to VCC) needed to enable the
device. Note that the device is fully enabled at VCC – 1.3 Vdc.
Figure 4 shows the relationship of enable current, Ienable to
enable voltage, Venable.
Mixer
The mixer is a double–balanced four quadrant multiplier
and is designed to work up to 500 MHz. It has a single ended
input. Figure 5 shows the mixer gain and saturated output
response as a function of input signal drive and for –10 dBm
LO drive level. This is measured in the application circuit
shown in Figure 15 in which a single LC matching network is
used. Since the single–ended input impedance of the mixer is
200 Ω, an alternate solution uses a 1:4 impedance
transformer to match the mixer to 50 Ω input impedance. The
linear voltage gain of the mixer alone is approximately 4.0 dB
(plus an additional 6.0 dB for the transformer). Figure 6
shows the mixer gain versus the LO input level for various
mixer input levels at 50 MHz RF input.
The buffered output of the mixer is internally loaded,
resulting in an output impedance of 1.5 kΩ.
Local Oscillator
The on–chip transistor operates with crystal and LC
resonant elements up to 220 MHz. Series resonant, overtone
crystals are used to achieve excellent local oscillator stability.
3rd overtone crystals are used through about 65 to 70 MHz.
Operation from 70 MHz up to 200 MHz is feasible using the
on–chip transistor with a 5th or 7th overtone crystal. To
enhance operation using an overtone crystal, the internal
transistor’s bias is increased by adding an external resistor
from Pin 29 (in 32 pin QFP package) to VEE to keep the
oscillator on continuously or it may be taken to the enable pin
to shut it off when the receiver is disabled. –10 dBm of local
oscillator drive is needed to adequately drive the mixer
(Figure 6). The oscillator configurations specified above are
described in the application section.
RSSI
The received signal strength indicator (RSSI) output is a
current proportional to the log of the received signal
amplitude. The RSSI current output is derived by summing
the currents from the IF and limiting amplifier stages. An
external resistor at Pin 25 (in 32 pin QFP package) sets the
voltage range or swing of the RSSI output voltage. Linearity
of the RSSI is optimized by using external ceramic bandpass
filters which have an insertion loss of 4.0 dB. The RSSI circuit
is designed to provide 100+ dB of dynamic range with
temperature compensation (see Figures 7 and 23 which
show the RSSI response of the applications circuit).
RSSI Buffer
The RSSI buffer has limitations in what loads it can drive.
It can pull loads well towards the positive and negative
supplies, but has problems pulling the load away from the
supplies. The load should be biased at half supply to
overcome this limitation.
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MOTOROLA ANALOG IC DEVICE DATA
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