The following diagram is a practical diagram for derivation of the clock signal from the received waveform itself (Synchronization) in baseband PAM systems.

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I'm looking for a typical circuit for the "Transistor current switches". I have no Idea of how it should be designed.

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    \$\begingroup\$ You need a couple of opposing current sources (source and sink if you like) switched by the two gate outputs. These could be simple 1 transistor sources, but they must be fast enough for your pulses. There is not timing scale on Fig. 5.23 \$\endgroup\$ – user1582568 Jan 20 '16 at 17:24
  • \$\begingroup\$ I note that on a previous question you raised (that I answered) you were unable to follow-up my final comment - from this I conclude you understood my answer. Here is the link: electronics.stackexchange.com/questions/200917/… - maybe you can either comment further or mark my answer as accepted? \$\endgroup\$ – Andy aka Jan 20 '16 at 18:30
  • \$\begingroup\$ @Andyaka You're true. I'll post a comment there for you. \$\endgroup\$ – SMA.D Jan 20 '16 at 20:25

The circuit labelled "transistor current switches" is called Charge Pump. Here is a "textbook" (ideal) implementation:


simulate this circuit – Schematic created using CircuitLab

M2 and M1 are the "switches". M3 and M4 establish the current being injected into or pulled out of the output. M5 and M6 are for the current reference, which establishes the gate voltages for M3 and M4 for the desired current (set by the current source).

The way it works is that when M2 is on, charge is injected to the output capacitor increasing the voltage linearly with time. When M1 is on (and M2 is off) the output capacitor is discharged at the same speed.

Depending on the requirements of the system, you might be able to get away by simply replacing M3 and M4 with resistors, but the current will be dependent on the voltage held at the capacitor.

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    \$\begingroup\$ Depends on your specs. As I said, you may just need 2 resistors and 2 MOSFETS if Vout will not change by much (that depends on your design). Usually charge pumps are integrated within a phase-locked loop (PLL) IC, which is what your circuit is. A clock recovery circuit is just a specialized PLL. See datasheets.maximintegrated.com/en/ds/MAX3676.pdf. The charge pump circuit is too simple to integrate in an IC. \$\endgroup\$ – jpcgt Jan 20 '16 at 19:47

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