Volt controlled

By changing the supply voltage fed to a classic 4584 Schmitt trigger type oscillator, the oscillator frequency can be changed over a range of 50:1. A 74HCU04 inverter is used at the output of the 4584 to maintain a constant TTL logic level signal...

The VFC (voltage-to-frequency-converter) circuit in Figure 1 achieves a wider dynamic range and a higher full-scale output frequency100 MHz with 10% overrange to 110 MHzby a factor of 10 over any commercially available converter...

The frequency comparator in Figure 1 uses two VCOs. C1, R1+R2, and the voltage at pin 9 determine the frequency of IC1 (900 Hz). C3, R5+R6, and the voltage at pin 9 determine the frequency of IC2 (1580 Hz). If fIN is lower than 900 Hz, then the output P2 of phase-comparator 2 in IC1 is high and drives the inhibit input of IC2 high via the R4-C2 lowpass filter. Consequently, the VCO in IC2 turns off. fIN is therefore higher than IC2`s frequency (0 Hz), so the output P2 of phase-comparator 2 in IC2 goes low, pulling the output low via the R8-C4 lowpass filter...

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC`s power supply VDD. The converted 8-bit data determines the duration of output high and output low...

The traditional frequency multiplier requires many elements: a phase comparator to detect the phase error between the input and the output signals, a lowpass filter to convert the phase error to a dc control signal, a VCO to generate the output, and a divider to set up the multiple ratio. The circuit in Figure 1 uses a different approach to multiply frequency with a programmable multiple ratio from 1 to 7 (Table 1)...

A project required an inexpensive oscillator whose frequency increased step by step from 200 to 400 Hz and then decreased to 200 Hz. The first step was to design a VCO with a staircase driver. However, this approach entailed at least four ICs and many discrete components. An alternative method (Figure 1) requires only one 16-pin µC (an MC68HC705KJ1, costing less than $1) and only a few external components...

The aircraft communication in Sweden is still Amplitud Modulated (AM). The local airport (Axamo) use the frequency 118.250 MHz. The reveiver I will explain is a tunable AM-receiver for this frequency. The receiver is instead manually tunable with some 100kHz around the 118MHz. The output from the receiver is a low level output (100-200mV) so you must connect it to some kind of amplifier. I will not explain how to build an audio-amplifier. The hart of the receiver is the Voltage Controlled Oscillator (VCO)...

The circuit in Figure 1 uses a Microchip 8-pin µC (PIC12C671) as a voltage-controlled oscillator (VCO). Because the PIC12C671 has an internal 4-MHz oscillator, four-channel 8-bit A/D converters, and built-in power-reset circuitry, you need no external components to configure the VCO. The µC reads two analog inputs through AN0 and AN1. The reference voltage for the A/D conversion is the µC`s power supply VDD...

In theory, synchronous clock multiplication is an easy task. A simple PLL with two digital dividersone inserted just after the VCO (voltage-controlled oscillator) and the second one placed directly at the input of the phase detectormay do the job. The flexibility of such a configuration allows for clock multiplication by any rational number...

A clock-recovery architecture can operate with NRZ digital signals, even at low SNRs. A clock-recovery subsystem is based on a PLL comprising a phase comparator, a loop filter, and a voltage-controlled oscillator (VCO)...

PLLs are useful in a variety of applications, most notably cable and TV tuners. In these systems, the PLL synchronizes an output signal (typically from a VCO) with a reference or input signal, in frequency as well as in phase. The VCO in these PLLs requires a biasing circuit...