# Signal / frequency / function generator 0.1Hz-200kHz (sine, square, and triangle)

A simple (fully analog) frequency generator can be build by the help of a 4 channel op-amp ()LMH6644), 6 transistors and a few passive components. The symmetrical power supply ( /-5-12V) is done using either a transformer or a charge pump. (The circuit can be used as discrete replacement for MAX038, ICL8038, XR2206, IA338D )

#### Basic circuit

Signal generator basic circuit

The circuit is based on a triangle/rectangle generator combination (IC3A IC3C). The frequency-range is given by the capacity values C14-C19 connected in the feedback, the exact frequency adjustment is done via the proportional feedback of the square wave signal back on the triangle generator.

#### Sinussynthetisator

The sine wave signal is produced by a "Sinussynthetisator". At f = 1kHz, a distortion factor of about k = 0.5% is achieved. Basic element of the sine former is the differential amplifier (Q3 Q4), whose emitter currents are provided by the current-controlled current source (Q5 Q6). Since differential amplifiers without current feedback are only linear at low signal input voltage regarding differencies between input voltage and output current, there is a weak current feedback done via R13. Its value depends on the collector current of the transistor Q6.

It applies:

At this circuit sizing, the peak R21 symmetrical triangle voltage must meet the following condition:

For this purpose varying R18 until the THD sine output voltage reaches a minimum.

The transistors Q3 / Q4 operate the collector side of the current mirror Q1 / Q2, the collector current difference of the collector current sum of Q1 / Q3 corresponds, which flows into the inverting input of the operational amplifier IC3D and at the output provides a sinusoidal voltage whose amplitude is proportional to the product of amount of current sum and the sum of the resistors R19 / R20 is.

Sources:
Mikroelektronik in der Amateurpraxis 2 (1.Auflg. 1984); Militärverlag der DDR
Kühne/, C. : Einfaches Sinusfunktionsnetzwerk, radio fernsehen elektronik 31 (1982) Heft 10, Seite 662-663
Kühne/, C. : Begrenzer für Sinussynthetisatoren, radio fernsehen elektronik 28 (1979) Heft 7, Seite 431-433

AGML battery charger

Simulation of synthesis of sinus 10 kHz

Simulation 1 Hz sinewave synthesis

The following diagram shows a simple linear power supply.

Signal generator linear power supply

Combining both, the wiring diagram is given by:

Signal generator schematic v1

PCB type 1

Signal generator PCB V1

PCB version 2 at 50x50mm.

Signal generator V2 PCB

If you have not symmetrical power supply, the negative operating voltage can be generated, for example, with a charge pump - there are several possibilities.

#### Timer 555 linear regulator LM337

Below some considerations with 555 and LM337 as shunt regulator.

10 kHz bipolar 555

10 kHz bipolar 555 regulation

10 kHz CMOS 555 push-pull

#### LM386 LM337

Alternatively to the timer 555, an LM386 are used in self-oscillating circuit, as shown in the following consideration.

LM386 inverter

The input-side current peaks at load currents &gt; = 100mA can be minimized by a circuit modification, as the following comparison shows. (R1/C1 released, R1 therefore, because of the LM386 is already internal base resistors)

LM386 comparison Inverter - circuit Variant 1

LM386 comparison Inverter - circuit Variant 2

Through the use of an input-side inductor capacitor, the efficiency at light loads may slightly be improved (probably not relevant in practice) - at the expense of a larger voltage drop at higher loads.

Parameters Würth inductor L1

LM386 comparison Inverter - circuit variant 3

Finally, as the following comparison shows, current transients can be attenuated with a series inductance at the output of the inverter when needed. (Probably not relevant in practice)

LM386 comparison Inverter - circuit variant 4

LM386 comparison Inverter - circuit variant 5

Thus combined schematic results to:

Signal generator schematic V2

Signal generator PCB V3

Further discussion on stromrichter.org.

### 3 responses

1. Mauro M says:

Hello!

Could you please give the PCB file signal generator?
Thank you!

2. Mauro M says:

Hello,

Congratulations for the good function generator project.
It is possible to provide the PCB file for fabrication of the PCB?

Thank you very much!

Mauro