MC3363 查看數據表（PDF） - Motorola => Freescale

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MC3363

LOW POWER DUAL CONVERSION FM RECEIVER

Motorola => Freescale 

MC3363

CIRCUIT DESCRIPTION

The MC3363 is a complete FM narrowband receiver from

RF amplifier to audio preamp output. The low voltage dual

conversion design yields low power drain, excellent

sensitivity and good image rejection in narrowband voice and

data link applications.

In the typical application, the input RF signal is amplified

by the RF transistor and then the first mixer amplifies the

signal and converts the RF input to 10.7 MHz. This IF signal

is filtered externally and fed into the second mixer, which

further amplifies the signal and converts it to a 455 kHz IF

signal. After external bandpass filtering, the low IF is fed into

the limiting amplifier and detection circuitry. The audio is

recovered using a conventional quadrature detector.

Twice-IF filtering is provided internally.

The input signal level is monitored by meter drive circuitry

which detects the amount of limiting in the limiting amplifier.

The voltage at the meter drive pin determines the state of the

carrier detect output, which is active low.

APPLICATIONS INFORMATION

The first local oscillator is designed to serve as the VCO in

a PLL frequency synthesized receiver. The MC3363 can

operate together with the MC145166/7 to provide a two-chip

ten–channel frequency synthesized receiver in the 46/49

cordless telephone band. The MC3363 can also be used with

the MC14515X series of CMOS PLL synthesizers and

MC120XX series of ECL prescalers in VHF frequency

synthesized applications to 200 MHz.

For single channel applications the first local oscillator can

be crystal controlled. The circuit of Figure 4 has been used

successfully up to 60 MHz. For higher frequencies an

external oscillator signal can be injected into Pins 25 and/or

26 — a level of approximately 100 mVrms is recommended.

The first mixer′s transfer characteristic is essentially flat to

450 MHz when this approach is used (keeping a constant

10.7 MHz IF frequency). The second local oscillator is a

Colpitts type which is typically run at 10.245 MHz under

crystal control.

The mixers are doubly balanced to reduce spurious

responses. The first and second mixers have conversion

gains of 18 dB and 21 dB (typical), respectively. Mixer gain is

stable with respect to supply voltage. For both conversions,

the mixer impedances and pin layout are designed to allow

the user to employ low cost, readily available ceramic filters.

Following the first mixer, a 10.7 MHz ceramic bandpass

filter is recommended. The 10.7 MHz filtered signal is then

fed into the second mixer input Pin 21, the other input Pin 22

being connected to VCC.

The 455 kHz IF is filtered by a ceramic narrow bandpass

filter then fed into the limiter input Pin 9. The limiter has 10 µV

sensitivity for – 3.0 dB limiting, flat to 1.0 MHz.

The output of the limiter is internally connected to the

quadrature detector, including a quadrature capacitor. A

parallel LC tank is needed externally from Pin 14 to VCC. A 68

kΩ shunt resistance is included which determines the peak

separation of the quadrature detector; a smaller value will

lower the Q and expand the deviation range and linearity, but

decrease recovered audio and sensitivity.

A data shaping circuit is available and can be coupled to

the recovered audio output of Pin 16. The circuit is a

comparator which is designed to detect zero crossings of

FSK modulation. Data rates of up to 35000 baud are

detectable using the comparator. Best sensitivity is obtained

when data rates are limited to 1200 baud maximum.

Hysteresis is available by connecting a high-valued resistor

from Pin 17 to Pin 18. Values below 120 kΩ are not

recommended as the input signal cannot overcome the

hysteresis.

The meter drive circuitry detects input signal level by

monitoring the limiting of the limiting amplifier stages.

Figure 5 shows the unloaded current at Pin 12 versus input

power. The meter drive current can used directly (RSSI) or

can be used to trip the carrier detect circuit at a specified

input power.

A muting op amp is provided and can be triggered by the

carrier detect output (Pin 13). This provides a carrier level

triggered squelch circuit which is activated when the RF input

at the desired input frequency falls below a present level. The

level at which this occurs is determined by the resistor placed

between the meter drive output (Pin 12) and VCC. Values

between 80 – 130 kΩ are recommended. This type of squelch

is pictured in Figures 3 and 4.

Hysteresis is available by connecting a high-valued

resistor Rh between Pins 12 and 13. The formula is:

Hyst = VCC / (Rh x 10 – 7) dB

The meter drive can also be used directly to drive a meter

or to provide AGC. A current to voltage converter or other

linear buffer will be needed for this application.

A second possible application of the op amp would be in a

noise triggered squelch circuit, similar to that used with the

MC3357/MC3359/MC3361B FM IFs. In this case the op amp

would serve as an active noise filter, the output of which

would be rectified and compared to a reference on a squelch

gate. The MC3363 does not have a dedicated squelch gate,

but the NPN RF input stage or data shaping comparator

might be used to provide this function if available. The op

amp is a basic type with the inverting input and the output

available. This application frees the meter drive to allow it to

be used as a linear signal strength monitor.

The circuit of Figure 4 is a complete 50 MHz receiver from

antenna input to audio preamp output. It uses few

components and has good performance. The receiver

toperates on a single channel and has input sensitivity of

0.3 µV for 12 dB SINAD.

NOTE: For further application and design information, refer to AN980.

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MOTOROLA ANALOG IC DEVICE DATA

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