# Pulse signal to sine signal with the same frequency

I have a pulse signal with frequency f(t) And i want to generate from it a sine signal with frequency f(t) (f(t) doesn't vary a lot in time) Is there a method to do it directly with a function generator ? If no, How can i acheive this?

• Are you looking for a frequency modulator?
– MBaz
Mar 7 at 22:49
• I think no, a frequency modulator will generate a sine signal with a frequency f(t) proportional to the amplitude of the pulse signal. What i need is a sine signal with the same frequency of the pulse signal. Mar 7 at 22:53
• Besides using a PLL as Marcus suggests, it might be worth it to see if the first harmonic of the pulsed signal also has frequency $f(t)$. If that is so, a simple low-pass filter would suffice.
– MBaz
Mar 8 at 13:59

Sounds like a very classical application of a PLL to me, aiming for the positive-going zero crossings of the sine wave emitted by a controllable oscillator to align with the position of these pulses

Assuming you ask this in an electronics, continuous-time context, implementation would look something like this:

1. Have a VCO running at roughly the right frequency¹.
2. Have a transmission gate (or analog mux, whatever) that gets activated for a controlled short time by every second of your input pulses (divide-by-2 with a flipflop), and which only then lets through the instantaneous value output by your VCO
3. Have an integrator / low pass filter to convert these pulses to the control voltage of your VCO

Alternative approaches that can be more power-efficient and faster to build in CMOS technology² would instead

2. convert your pulse train to a binary square wave (e.g., only 0 V and +1 V) by means of a toggle flip-flop
3. convert your VCO's sine to a similar square wave by comparing it to its average voltage (0 V)
4. combine the two with an XOR gate: if they are both at exactly the same frequency and phase-aligned, it will always output 0
5. when the XOR output is
• low / 0: output zero
• high/ not 0: either output a positive or negative voltage, depending on the state of the flip-flop output