FIGURE 8 - RELATIVE MIXER GAIN
~
DERIVED USING OPTIMUM UC
FIGURE 5 - LIMITING I.F. FREQUENCY RESPONSE
-10
I I
IF OUTPUTR~SpJNJE ~A~l~ ~N
- A SPECIAL PROTOTYPE.
_ TERMINALS NOT
FIGURE 7 - DETECTOR AND AFC RESPONSES 8.0 RELATIVE FREQUENCY [kHz[
FIGURE 9 - OVERALL GAIN, NOISE, AND A.M. REJECTION 10
III IIIIIIIIIIII
S+N+-I';'"3KH FM
MOTOROLA COMMUNICATIONS DEVICE DATA
FIGURE 10 - OUTPUT COMPONENTS OF SIGNAL, NOISE, AND DISTORTION
111111 II III
~ fa = 10.7 MHz
0; -10 f--I''I'W-t+I-HtI--H-H+ltttl-H-H-I+H+H--I-H fm = I kHz
:!;!. I1f = :!:3.okHz
!3 20 I-+H+tl~++-+I-H+Ht-f-t-t+1-tHlH-+-+I TEST CIRCUIT OF
!5 -
~ FIGURE 3.o ~ - 3D H-H-t+I-HtI---H'Nc1+1tttl-H-I N + 0 f-t-t+1-ttffi+1+t+H1tI
~ TIffirrrr~lffitr~~~-H-H~
~ -40 IIIII
I~"
- 50
~1+tlJI--.1...t-~t-J.=t:I:j::jjllll#=l=l=l=l=f:I##=I=l==F##1ll
-~o~ol~~llllo~.o~I~~llWo.'-W~~WI.~o~~lllll~o~-w~w,oo
FIGURE 12 - UC OSCILLATOR, TEMPERATURE AND POWER SUPPLY SENSITIVITY
Vcc. SUPPLY VOLTAGE IVdcl
58 59 60 61
AM81ENT TEMPERATURE I'CI
FIGURE 14 - UC OSCILLATOR RECOMMENDED COMPONENT VALUES CURRENT DRAIN versus SUPPLY VOLTAGE
~UOIO O~TPUT
Vcc. SUPPLY VOLTAGE IVdcl
8.0
o
401--l--HH+ttll
tFII
",-+-+-P\.!:/'IIl---'>,d-H-++FOR OPEN lOOP GAIN! IIII p::::..
~ AND PHASE ISOLID lINESI"-Dr-VCC:: '6.0Vd~'--t-++ttHllt---+-+++ttltf--+-+-f"kHftti 3D
Dr-I
11111111.0 K 10 K 100 K
FREQUENCY IHzl
l.oM 10M AIloJ = GAIN AT CENTER FREQUENCY
O'17~OOl"12
- R3 = 'I\' f~Cl Vrms 18K -:-1500 R2 V,e! + ":' Voul
OSCILLATOR FREQUENCY IMHzl
MOTOROLA COMMUNICATIONS DEVICE DATA
7
~s: UlO I\:IW
m
§
:0
o s;
8 :s::
:s::
c
z
(')
:!:;
o z en o
~ (') m
o
~
»
r-~---~---r---,
13~
?14,.
33 k
V
~C6-'I "'-l
33 k ~ 33 k 3.5 k 33k~ 33 k
012 013 '014
12
~63
061
15k 062( 1k
(
3.5
k
II!~ ~50 kl
065 I III
~3
071 066
070 06~
068r069
50 kS 2.5 k 750 U I
072
50 k
OSCILLATOR - MIXER : OP AMP (BROADCAST DETECTOR
---~---~---r-17
LIMITING IF AMPLIFIER
m4 . ,
022" " " " ,
0189lOOk 110 k 019·
021 10 k
10 k 10 k 10 k 10 k
33 k 33 k 33 k 33 k
DETECTOR AND AFC
_9
50 k
33 k 10 k 1~) 33k 5 k 057'
L _________________________________
~ -I___________________
-FIGURE 16 - CIRCUIT SCHEMATIC
CIRCUIT DESCRIPTION
The MC3359 is a low-power FM IF circuit designed primarily for use in voice-communication scanning receivers. It is also finding a place in narrowband data links.
In the typical application (Figure 1), the mixer-oscillator com-bination converts the input frequency (10.7 MHz) down to 455 kHz, where, after external bandpass filtering, most of the am-plification is done. The audio is recovered using a conventional quadrature FM detector. The absence of an input signal is in-dicated by the presence of noise above the desired audio fre-quencies. This "noise band" is monitored by an active filter and a detector. A squelch-trigger circuit indicates the presence of noise (or a tone) by an output which can be used to control re-spectively. The crystal is used in fundamental mode, calibrated for parallel resonance at 32 pF load capacitance. In theory this means that the two capacitors in series should be 32 pF, but in fact much larger values do not significantly affect the os-cillator frequency, and provide higher osos-cillator output.
The oscillator can also be used in the conventional UC Col-pitts configuration without loss of mixer conversion gain. This oscillator is, of course, much more sensitive to voltage and temperature as shown in Figure 12. Guidelines for choosing L and C values are given in Figure 14.
The mixer is doubly balanced to reduce spurious responses.
The mixer measurements of Figure 4 and 6 were made using an external 50 fl source and the internal 1.8 k at Pin 3. Voltage gain curves at several VCC voltages are shown in Figure 4. The Third Order Intercept curves of Figure 6 are shown using the conventional dBm scales. Measured power gain (with the 50 fl input) is approximately 18 dB but the useful gain is much higher because the mixer input impedance is over 3 kfl. Most applications will use a 330 fl 10.7 MHz crystal filter ahead of
MOTOROLA COMMUNICATIONS DEVICE DATA
has an internal 1.8 k resistor. The IF has a 3 dB limiting sen-sitivity of approximately 100 /LV at Pin 5 and a useful frequency range of about 5 MHz as shown in Figure 5. The frequency limitation is due to the high resistance values in the IF, which were necessary to meet the low power requirement. The out-put of the limiter is internally connected to the quadrature de-tector, including the 10 pF quadrature capacitor. Only a parallel UC is needed externally from Pin 8 to VCC. A shunt resistance can be added to widen the peak separation of the quadrature detector.
The detector output is amplified and buffered to the audio output, Pin 10, which has an output impedance of approxi-matley 300 fl. Pin 9 provides a high impedance (50 k) point in the output amplifier for application of a filter or de-emphasis capacitor. Pin 11 is the AFC output, with high gain and high output impedance (1 M). If not needed, it should be grounded, or it can be connected to Pin 9 to double the recovered audio.
The detector and AFC responses are shown in Figure 7.
Overall performance of the MC3359 from mixer input to au-dio output is shown in Figure 9 and 10. The MC3359 can also be operated in "single conversion" equipment; i.e., the mixer can be used as a 455 kHz amplifier. The oscillator is disabled by connecting Pin 1 to Pin 2. In this mode the overall perfor-mance is identical to the 10.7 MHz results of Figure 9.
A simple inverting op amp is provided with an output at Pin 13 providing dc bias (externally) to the input at Pin 12, which is referred internally to 2.0 V. A filter can be made with external impedance elements to discriminate between frequencies.
With an external AM detector, the filtered audio signal can be checked for the presence of either noise above the normal audio, or a tone signal.
The open loop response of this op amp is given in Figure 13. Bandpass filter design information is provided in Figure 15.
A low bias to Pin 14 sets up the squelch-trigger circuit such that Pin 15 is high, a source of at least 2.0 mA and the audio mute (Pin 16) is open-circuit. If Pin 14 is raised to 0.7 V by the noise or tone detector, Pin 15 becomes open circuit and Pin 16 is internally short circuited to ground. There is no hysteresis.
Audio muting is accomplished by connecting Pin 16 to a high-impedance ground-reference point in the audio path between Pin 10 and the audio amplifier. No dc voltage is needed, in fact it is not desirable because audio "thump" would result during the muting function. Signal swing greater than 0.7 V below ground on Pin 16 should be avoided.
MC3359 2-53
MOTOROLA
- SEMICONDUCTOR
TECHNICAL DATA
Advance Information
LOW POWER NARROWBAND FM IF
The MC3361 B includes an Oscillator, Mixer, Limiting Amplifier, Quadrature Discriminator, Active Filter, Squelch, Scan Control, and Mute Switch. This device is designed for use in FM dual conversion communications equipment.
• Operates From 2.0 V to 8.0 V Supply
• Low Drain Current 3.9 mA Typ (W VCC
=
4.0 Vdc• Excellent Sensitivity: Input Limiting Voltage --3.0 dB = 2.6 /LV Typ
• Low Number of External Parts Required
• Operating Frequency Up to 60 MHz
FIGURE 1 - FUNCTIONAL BLOCK DIAGRAM
Scan Squelch Filter Filter Recovered Gnd Mute Control In Output Input Audio
Crystal Osc
Decoupling Coil
This document contains information on a new product. Specifications and information herein are subject to change without notice.
MC3361B 2-54