SL623 Zarlink Semiconductor Inc, SL623 Datasheet - Page 3

• Manufacturer Part Number: SL623
• Description: AM DETECTOR/ AGC AMPLIFIER & SSB DEMODULATOR
• Manufacturer: Zarlink Semiconductor Inc

SL623
ELECTRICAL CHARACTERISTICS
NOTES
1.The AGC range is the change in input level to increase AGC output voltage from 2.0V to 4.6V
APPLICATION NOTES
AGC Generator
decoupled to ground by a 1 microfarad capacitor (C4),
keeping leads as short as possible The value of C4 is quite
critical, and should not be altered: if it is increased the
increased phase shift in the AGC loop may cause the receiver
to become unstable at LF and if it is reduced the modulation
level of the incoming signal will be reduced by fast-acting
AGC.
amplifiers. The SL623AGC output is an emitter follower
similar to that of the SL621C. Hence the outputs of the two
devices may be connected in parallel when constructing AM/
SSB systems.
AM detector. In a combined AM/SSB system, therefore, the
signal will automatically produce an SSB AGC voltage via the
SL621C as long as a carrier (BFO) is present at the input to the
SSB demodulator of the SL623C. The AGC generator of the
SL623 will not contribute in such a configuration.
carrier input of the SSB demodulator. In the absence of an
input signal, the SL621C will then return to its quiescent state.
To switch over a receiver using the SL623C from SSB to AM
operation it is therefore necessary to turn off the BFO and
transfer the audio pick-off from the SSB to the AM detector.
operation can result in heterodyning due to pick-up of carrier
on the input signal In some sets different filters are used for AM
and SSB: these will also need to be switched.
Supply current
Input impedance
SSB audio output
AM audio output
AGC range (Note 1)
Pin 3, the AGC amplifier phase correction point should be
The AGC output (Pin 4) will drive at least two SL610/11/ 12
Less signal is needed to drive the SSB demodulator than the
For AM operation the BFO must be disconnected from the
Neglecting to disconnect the SSB carrier input during AM
The 10 kilohm gain-setting preset potentiometer is adjusted
Test conditions (unless otherwise stated)
Supply voltage V
Ambient temperature: -30 C to +85 C
Test circuit as Fig.2
Characteristics
CC
= 6V
Min.
22
43
Value
Typ.
800
30
55
9
Max.
11
47
67
6
ABSOLUTE MAXIMUM RATINGS
so that a DC output of 2 volts is achieved for an input of 125mV
rms There will then be full AGC output from the SL623C for a
4dB increase in input. A fixed resistor of 15kilohms can often
be used instead of the potentiometer.
SSB Demodulator
capacitor It should have an amplitude of about 100mV rms and
low second harmonic content to avoid disturbing the DC level
at the detector output.
a 0.01 microfarad capacitor. The output impedance of the
detector is 3 kilohm and the terminal is at a potential of about
+2V which may be used to bias an eminer follower if a lower
output impedance is required. The input to the audio stage of
a receiver using an SL623C should be switched between the
AM and the SSB outputs — no anempt should be made to mix
them. Since the SL621C is normally used in circumstances
where low-level audio is obtained from the detector, the
relatively high SSB audio output of the SL623C must be
attenuated before being applied to the SL621C. This is most
easily done by connecting the SL623C to the SL621C via a 2
kilohm resistor in series with a 0.5 microfarad capacitor.
Input Conditions
Connection must be made to the input via a capacitor to
preserve the DC bias. An input of about 125mV rms is required
for satisfactory carrier AGC performance and 20mV rms for
SSB detection. Normally, the AGC will cope with this variation
but in an extreme case a receiver using an SL623C and having
the same gain to the detector in both AM and SSB modes will
be some 10dB less sensitive to AM.
The carrier input is applied to Pin 6, via a low-leakage
Pin 8 is the SSB output and should be decoupled at RF by
The input impedance is about 800 ohms in parallel with 5pF
mVrms
mVrms
Units
Supply voltage: 12V
Storage temperature: -55 C to +125 C
mA
dB
No signal, Pin 4 open
Pins 6, 9
Signal input 20mVrms @ 1.78
MHz. Ref. signal input 100mV
@ 1.750MHz
Signal input 125mVrms @ 1.75MHz
modulated to 80% at 1KHz
Initial signal input 125mVrms at 1.75MHz
modulated to 80% at 1KHz. Output set to
2.0V with 10K potentiometer between
Pins 2 & 5
Conditions