Sailor RT2047 Technical Manual page 39

2 CIRCUIT DESCRIPTION RT2047 DSC - PART II
2.2.4 PHASE DETECTOR PUMP AND LOOP FILTER
We assume that the RX-VCO frequency has decreased from its nominal frequency, The phase-detector
now sends negative correction pulses from IC202 pin 17 to T210, which goes on. A current will then flow
from C225 through R225 and R229 and into T210. This current will discharge C225 forcing the output
voltage from the transistors T205 and T206 to increase until the VCO reaches the correct frequency. If
the RX-VCO frequency is too high, the negative correction pulses from the detector at pin 16 of IC202
will turn transistor T209 off. The collector voltage of transistor T209 increases and a current will flow
through the diode D202, the resistor R225 and into the capacitor C225 and charge this capacitor. The
output voltage at the collector of the transistors T205 and T206 will decrease until the VCO reaches its
right frequency. If the phase-locked-loop is locked, both outputs of the phase-detector will be 5 V and the
output voltage of the transistors T205 and T206 will have a value between 2 V and 10 V corresponding
to the VC0-frequency. However, the system is working with a constant phase error and the phase detector
sends small correction pulses to transistor T210, even the phase-locked-loop is locked. The four
transistors T205, T206, T207, and T208 are working as an operational amplifier with the inverting input
at base of transistor T208. Non-inverting input is at transistor T207 while the transistors T205 and T206
forms the output stage.
9543 PAGE 2-5