A very simple DCF77 module circuit can be designed using this circuit diagram, that is based on the MAS6180C1 integrated circuit, designed by MAS (Micro Analog Systems).
The MAS6180C1 is an AM-Receiver chip specially intended to receive time signals in the frequency range from 40 kHz to 100 kHz. Only a few external components are required for
time signal receiver. The circuit has preamplifier, wide range automatic gain control, demodulator and output comparator built in.
The control for AGC (automatic gain control) can be used to switch AGC on or off if necessary.
Because this is a DCF77 module circuit we need a 77.503khz crystal oscillator and a 77.5khz frequency tuned antenna, but the MAS6180 circuit can be used for many Time Systems Frequencies like : DCF77, HCB,MSF,WWVB,JJY,BPC.
For this DCF77 module we’ve used a TSSOP-16 package version of MAS6180C1 thanks to Micro Analog Systems.
Pin number 1 VDD is positive power supply, used to powering circuit.
Pin number 2 QOP Positive Quartz Filter Output ( connection for cristal oscillator)
Pin number 3 QOM Negative Quartz Filter Output, which is is electrically unconnected in MAS6180C1 version.
Pin number 5 QI Quartz Filter Input for Crystal ( connection for crystal oscillator))
Pin number 6 AGC AGC Capacitor (automatic gain control) it is recomanded that AGC capacitor to have low leakage current and a voltage arting at least 25V.
It is recommended to connect AGC capacitors to VDD although VSS connection is also possible. The VDD connection provides better supply noise immunity because signals are referenced to VDD.
Pin number 8 OUT Receiver Output ( output signal)
Pin number 9 DEC Demodulator Capacitor DEC capacitors specifications are same as AGC Capacitor
Pin number 10 AON AGC On Control, AGC circuit on all the time if AON pin is left unconnected.
AON = VSS means AGC off (hold current gain level); AON = VDD means AGC on (working)
Pin number 11 PDN, Power Down Input The device is in power down (turned off) if
PDN = VDD and in power up (turned on) if PDN = VSS.
Pin number 13 RFIP Positive Receiver Input
Pin number 15 RFIM Negative Receiver Input
Receiver inputs RFIP and RFIM are used to connect antenna terminals and have both 1.4 MW biasing resistors towards VDD
Pin number 16 VSS Power Supply Ground
All rest of pins are unconnected.
The ferrite antenna converts the transmitted radio wave into a voltage signal. It has an important role in determining receiver performance. Recommended antenna impedance at resonance is around 100 kW.
Low antenna impedance corresponds to low noise but often also to small signal amplitude.
Antenna impedance Rant can be calculated using equation 1 where fres, L, Qant and C are resonance frequency, coil inductance, antenna quality factor and antenna tuning capacitor respectively. Antenna quality factor Qant is defined by ratio of resonance frequency fres and antenna bandwidth B (equation 2).
For this module we’ve used a self made antenna made from ~0.23mm CuEm wire 2 layers on a ferrite rod.
Coil must have an inductance of about 1.95mH+/-10% and design specifications mentioned bellow.
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