Contents
How does a synth VCO work?
Voltage Controlled Oscillators (commonly referred to as VCOs) are used in synthesizers to convert a DC signal from the power supply into an AC signal, where the signal then oscillates at a certain frequency, generating a sound. The frequency of a VCO can be adjusted via input voltage or current modulation.
When might a voltage controlled oscillator VCO be needed?
Typical applications include communications systems, frequency chirps in radar, phase tracking in PLLs, and frequency hopping applications such as remote keyless entry (Figure 1).
On what parameters does the free running frequency of a VCO depend on?
The VCO is a free running multivibrator and operates at a set frequency fo called free running frequency. This frequency is determined by an external timing capacitor and an external resistor. It can also be shifted to either side by applying a dc control voltage vc to an appropriate terminal of the IC.
What is purpose of varactor diode?
Varactor or varicap diodes are used mainly in radio frequency or RF circuits to provide voltage controlled variable capacitance. These electronic componenta can be used in a whole variety of ways where a capacitance level needs to be controlled by a voltage.
What is VCO on a synth?
A voltage controlled oscillator, or VCO, is an oscillator whose output frequency is determined by an input control voltage. The VCO, or a digital equivalent of it, is an essential component of all modern synthesizers, and it serves as the primary sound source on most analog synthesizers.
What is the pulling range of a VCXO?
The pulling range is the ratio of the up (or down) frequency variation to the center frequency. This ratio is usually represented in ppm (part per million). This measurement provides the relative pulling range of VCXO. Normally, the pulling range is about 100ppm–200ppm, depending on the structure of VCXO and the selected crystal.
What makes a VCXO different from other oscillators?
Just like any other type of crystal oscillator, a VCXO uses vibrations from the crystal to generate a signal. What makes the VCXO unique is the use of diodes to tune the frequency of the signal, a process known as “pulling” the frequency, which is measured in parts per million (ppm).
How does loading capacitance affect the tuning range of VCXO?
For a small value of load capacitance, the VCXO tuning range is limited in upper side; likewise a large value of the capacitance reduces the tuning range in lower side. The right value of loading capacitance to use is depending on the character of the VCXO.
What can a VCXO clock generator be used for?
VCXO clock (CLK) generators have been used in various applications, such as digital TV, digital audio, ADSL, and STB. This application note provides the general structure for a VCXO CLK generator, key performance measurements, guidelines for PCB design, and a test setup for MAX9485, a VCXO CLK Gen chip for MPEG2 and AC-3 audio applications.