Volt controlled

VCO with NE567

Who would like to build a sidetone oscillator with a minimum amount of parts should try the NE567 integrated circuit. The NE567 is a PLL circuit with an internal VCO for a operating frequency less than 500 kHz and it is normally used as an audio tone decoder. The VCO frequency is adjustable by two passive components only. For a 750 Hz sidetone in an amateur radio application the capacitor C1 and the resistor R1 define the VCO frequency. The IC supplier allows for R1 a range of 2 .... 20 kOhm. The sidetone can be taken from pin 6 as a symmetrical triangle signal or as a high impedance square wave signal from pin 5. The triangle signal has an amplitude of 1 Vss and the square wave signal of 2 Vss. In order to switch on the oscillator during transmit mode Tx, one can connect pin 7 to Gnd or pin 4 to Vcc. Pins 1, 2, 3 and 8 remain free (nc). ..

Simple VCO with 1 transistor

Unijunction transistors are very intresting. They love to be used in oscillators, and it doesn't takes too many part or very much coaxing to get their sawtooth outputs. This litle squealer will tell you how much voltage it'a connected to. The higher the voltage, the lower frequency output you'll hear...

Voltage Controlled Oscillator with BF990A

The VCO is based on a Hartley oscillator. The frequency is determined by L1 and capacitor C1. The Vtuning voltage will change the capacitance in the varactor BB132 wich will change the oscillation-frequency. The value of capacitor C2 will determine how much the frequency can be changed by the tuning voltage. The larger value the more the frequency will change. This VCO is based on two dual-gate FET. First FET is a Hartley oscillator where the frequency is determined by the value of L1, C1, C2 and the varicap diod. C2 set the span of the VCO. The second FET is just an amplifier. The gain is less than 1, but the current will be higher and the oscillator will not be loaded. The output amplitud changes depending on the frequency and how many turns there is on L1. By changing the voltage on g2 at FET1 you can set the amplitud. By adding a resistor to ground you will lower the amplitud. In this schematic I have conected g2 to Vcc (through R1) wich will give the highest gain. ..

Voltage Controlled Oscillator 1.2GHz

Since high frequency voltage-controlled oscillators, or VCOs, are not easy to construct, Maxim (www.maxim-ic.com) has produced an integrated 1.2GHz oscillator, the MAX2754. The center frequency is set using the TUNE input, and a linear modulation input allows the frequency to be modulated. The IC is available in an 8-pin µMAX package, operates from a supply of between 2.7 V and 5.5 V, and draws a current of less than 2 mA. Both TUNE and MOD operate over control voltage range of +0.4 V to +2.4 V. TUNE allows the VCO frequency to be adjusted from 1050 MHz to 1270 MHz...

Here's another daft yet interesting PIC12F675 idea I came up with. When I wanted to show someone how logic gates worked I could only find a NAND gate which wasn't very handy for demonstrating AND's OR's, NOR's and ExOR's. I also wanted to have a play with the A/D converter on the 12F675 so I came up with the idea of a PIC that could function as a single 2-input logic element. The logic function is determined by an analogue voltage applied to the GPIO4 pin when the device is first reset, it isn't sampled again after this so logic can't be changed on the fly. The 3 MSBs of the A/D conversion give eight distinct voltage levels that map to specific logic functions...

Here is the latest and greatly improved TX200 VFO/VCO FM transmitter. The most versatile transmitter to date that can be turned into high fidelity stereo PLL based 200mW FM transmitter. It is a perfect circuit for transmitting your music around the house and yard. TX200 uses only two coils; one in the oscillator and the other one in the 200mW VHF amplifier so it should be fairly easy for anyone to build. It also includes built-in pre-emphasis and C5 for enhanced sound quality. While assembling the transmitter care must be taken to make sure that C1 is directly connected to L1 and C9 to L2. These caps eliminate the distortions form the DC supply and improve the sound quality greatly. 9V voltage supply is also very important because it provides the exact amount of current to Q1 to produce loud and clear sound quality...

This is a very simple circuit utilising a 555 timer IC to generate square wave of frequency that can be adjusted by a potentiometer. With values given the frequency can be adjusted from a few Hz to several Khz. To get very low frequencies replace the 0.01uF capacitor with a higher value...

This circuit was designed to frequency modulate a 40KHz carrier, using human voice frequencies. A common flip/flop is used at the core of the circuit...

The circuit`s simplicity, unconditional stability, and consistent high-drive capability over an octave make the oscillator ideal for many applications, such as synthesized sources, local oscillators, and transmitters. The AHC logic family (Texas Instruments, www.ti.com) makes the circuit`s performance possible. AHC is a relatively new line of CMOS logic whose high speeds and good noise performance allow oscillator operation into regions in which bipolar-junction-transistor and FET designs prevail...

Many portable RF products use VCOs to generate the RF carrier frequency. These applications often require low-noise VCO power-supply voltages that are higher than the primary battery voltage. Many designs use a dc/dc converter powering a low-noise linear regulator. This approach has several inherent disadvantages. The dc/dc converter produces noise that the regulator may not reject, resulting in regulator-output noise far greater than the thermal-noise levels...

The main purpose for building the circuit in Figure 1 is to study the idiosyncrasies of X5R, Z5U, and Y5V multilayer ceramic capacitors. The circuit is also an inexpensive VCO (voltage-controlled oscillator) with only five components. Many types of ceramic capacitors for surface-mount placement are on the market...

A VCO (voltage-controlled oscillator) is an analog circuit, so you cannot find it in the libraries for the design of digital programmable chips. When you need such a circuit for synchronization or clock multiplication, you need to find a circuit that works with the standard digital functions, such as AND and NAND. Several possibilities exist for building variable-frequency oscillators. For example, you can change the frequency using a varactor diode. Unfortunately, these diodes have a small change of frequency per volt...

The circuit in Figure 1 is a quadrature-output VCO that provides both positive and negative output frequencies, depending on the polarity of the control-voltage input. The circuit provides a function that designers traditionally implement in analog music-effects units, such as Bode/Moog frequency shifters. Bode/Moog shifters use fixed-beat-frequency oscillators at 20 kHz and variable sine oscillators that go higher and lower than 20 kHz. Both oscillators feed into mixers...

The circuit in Figure 1 illustrates a narrowband VCO, which has a digitally programmable center-frequency ratio of greater than 2-to-1. With a VCO having center-frequency ratio (F HIGH/FLOW) of greater than 2-to-1, you can derive any output frequency by simple binary division. The VCO has extremely high spectral purity, and typically operates at frequencies greater than 230 MHz by using high-performance ECL. Also, you can enable and disable the VCO almost instantaneously...

The output frequency of the simple VCO in Figure 1, which is synthesized from inverting latch stages, is tunable to an integer multiple of the input frequency by selecting which output phases feed back to the input multiplexer. The circuit has worked successfully in on-chip clock multiplication in ASICs. The number of latch stages that you can cascade in a real-world design limits the multiplication factor...