SL6654 Zarlink Semiconductor Inc, SL6654 Datasheet - Page 5

• Manufacturer Part Number: SL6654
• Description: LOWER POWER IF/AF CIRCUIT (WITH RSSI) FOR FM CELLULAR RADIO
• Manufacturer: Zarlink Semiconductor Inc

GENERAL DESCRIPTION
integrated circuit intended for IF amplification and
demodulation in FM radio receivers. It comprises:
Mixer
set externally by the load resistor although the value is
normally determined by that required for matching into the
ceramic filter. It is possible to use a tuned circuit but an
increase in mixer gain will result in a corresponding reduction
of the mixer input intercept point.
current of typically 300 A. The oscillator input is differential
but would normally be driven single-ended. Special care
should be taken to avoid accidental overload of the oscillator
input.
Oscillator
The oscillator consists of an uncommitted transistor and a
separate current sink. The user should ensure that the design
The SL6654 is a very low power, high performance
A mixer stage for use up to lOOMHz
An uncommitted transistor for use as an oscillator
A current sink for biasing this transistor
A limiting amplifier operating up to 1.5MHz
A quadrature detector with differential AF output
An RSSI (Received Signal Strength Indicator) output
The mixer is single balanced with an active load. Gain is
The RF input is a diode-biased transistor with a bias
8
16
REFERENCE
BAND-GAP
15
17
1
9
4k
40k
7
40k
3
4
Fig. 3 Internal schematic
2
10
18
of oscillator is suitable for the type of crystal and frequency
required; it may not always be adequate to duplicate the
design shown in this data sheet.
IF amplifier
MHz and the input impedance is set by an external resistor to
match the ceramic filter. Because of the high gain, pins 12 and
13 must be adequately bypassed.
Detector
the IF amplifier; the quadrature input is fed externally using an
appropriate capacitor and phase shift network. A differential
output is provided to feed a comparator for digital use,
although it can also be used to provide AFC.
RSSI output
proportional to the logarithm of the IF input signal amplitude.
There is a small residual current due to noise within the
amplifier (and mixer) but beyond this point there is a measured
and guaranteed 70dB dynamic range. The typical range
extends to 92dB, independent of frequency, and with
exceptionally good temperature and supply voltage stability.
13
14
12
The limiting amplifier is capable of operation to at least 1
A conventional quadrature detector is fed internally from
The RSSI output is a current source with value
200k
200k
BIAS
11
SL6654
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