A FUNCTION GENERATOR

I want to share my version of the functional generator frequency sweep for the home lab. Consuming from the electrical power source 50 mA, is a compact, fairly simple to manufacture, the device generates periodic signals are sinusoidal, rectangular, triangular, and rectangular pulses for testing and tuning of the instrument, made on modern element base.

 

This, of this design due to the use of the chip К174ГФ2 (analogue XR2206), “specialization” which is to serve as a voltage controlled oscillator of various shapes — amplitude, frequency and phase modulator; and to act as a component of the tracking filters, synchronous detectors and low-frequency systems, phase-locked loop.

 

When applying the sawtooth with an oscilloscope at the input 1 (see the schematic diagram of the proposed device) is the frequency deviation of any of the forms. The signals are generated in the range from 4 Hz to 30 kHz (for a rectangle) and up to 490 kHz (sine and triangle).

 

The whole frequency band is divided into five decades (ranges). Adjustment of the frequency within each of them— smooth. Deviation of the selected frequency is not less than ±8%. The respective variable resistors sets the amplitude of the signal: 0 to 10 V — for a rectangular to a 4—triangular, up to 1.8 V for sinusoidal shapes. Provided (“shells” out.H) and adjusting the amplitude of the rectangular pulses used to test digital devices in CMOS and TTL circuits. Imposed limits changes here from 0 to 10 V.

 

Circuit design this function generator is such that harmonic distortion of the sine wave is less than 0.7%, the coefficient of nonlinearity of triangular signal of -1.5% and the rise time and fall of the rectangular pulses is not more than 0.1 µs. Output impedance on out. 1 is 25 Ohms at the output.2-300 and out.S—20 Ohms.

 

 

A circuit diagram and a printed circuit Board, a homemade function generator frequency sweep

 

To improve the shape of a rectangle in the design introduced a Schmitt trigger, implemented on the chip DD1. The transistors are connected so that VT1 operates as the input of the sawtooth amplifier and VT2 — VT4 perform the functions of emitter repeaters.

 

The waveform on out.1 depends on the switch SA1. With closed contacts, the latter is the sine wave, and when open— continuous series of triangular pulses. SA2 is used to switch ranges. Smooth speed control is a variable resistor the FREQUENCY and deviation — other “shells” with an appropriate inscription.

 

Almost the entire generator (with the exception of variable resistors, switches, capacitors C5-C9 Yes sockets input / output signal) mounted on the PCB of one-sided foil fiberglass 95x51x1,5 mm. Most of the electronic components — the most that neither is common.

 

So, as the fixed resistors will be suitable, for example, the MLT-0,125; for the “peremennikami” RZ, R8, R18, R20, R21 will fit much less well-known SPZ-or SPZ 4A-9a; well in the role of “trimmers” R11, R13 and R14 is acceptable SP5-3, SP5-16. Capacitors C1 — C4, C10 — C12, C14 from the category of deficient. In particular, suitable here “electrolytes” K50-6. The remaining capacitors can be of any type; however, preferably, C5 — C9, is mounted directly on the range switch, had besides thermostable settings.

 

Typically, the generator, assembled correctly and a known good electronic components, special setup is not required. But sometimes it can be considered justified and small adjustments. In particular, when the “postroeniem” R13 achieve almost perfect shape from a sine wave. Through R14 is adjusted symmetric, and R11 exhibited the desired amplitude at the output.1 function generator.

 

Make yourself such a device for home lab — you will not regret!

 

V. GRICHKO, Krasnodar