Voltage to Frequency

Figure 1, below, shows the 10.58 to 10.74 MHz VFO oscillator circuit. Yes, this is the same circuit that was presented last time, but I’ve re-drawn it to show the Colpitts oscillator more clearly. "L" is approximately 1.5 uH; 19 turns in a T50-6 core (yellow). The value of C6 is found experimentally. I used 69 pF (a 47 pF and a 22 pF in parallel). More about this during check-out.

Figure 1 shows a voltage-to-frequency (V/F) converter that produces a 0- to 10-kHz output for an input range of 0 to 5V. Linearity of the converter is 0.02%, and gain drift is 60 ppm/8C. The maximum current consumption is only 26 µA, 100 times lower than currently available units. To understand the circuit's operation, assume that the voltage at IC1's negative input is lower than the voltage at its positive input (IC2's output is low).

This application note is intended to show a general solution for implementing a low cost A/D and a 2-way multiplexed LCD drive using National Semiconductor's COP840C 8-bit microcontroller. The implementation is demonstrated by means of a digital personal scale. Details and function of the weight sensor itself are not covered in this note.

No description available.

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.

If you need a clean emitter coupled logic (ECL) type signal between 200MHz and 400MHz this circuit works fine. It uses four voltage-controlled capacitors to change the frequency.

This circuit uses a CMOS version of the classic 555 timer, to form a light intensity to frequency converter. A small PIN photo diode is used as the light detector. The pulses produced are short, so in some applications you may want to stretch them or feed them through a flip/flop to produce a square wave signal. Although the circuit shown is designed for a 5v supply, it could operate from almost any voltage from 3v to 15v.

Single-phase induction motors are extensively used in appliances and industrial controls. The Permanent Split Capacitor (PSC) single-phase induction motor is the simplest and most widely used motor of this type. The classification, construction and working principle of single-phase induction motors are explained in detail in the application note "AC Induction Motor Fundamentals" (AN887) available from Microchip.

The best of the monolithic voltage-to-frequency (V/F) converters have performance that’s so good it equals or exceeds that of modular types. Some of these ICs can be designed into quite a variety of circuits because they’re notably versatile.

The inspiration for the VCO in Figure 1 came from Texas Instruments’ application notes of years ago, detailing the use of unbuffered U-type inverters for use in ring oscillators. The application note’s circuit consists of only the inverters. The circuit generates relatively squarish waveforms. Any ring oscillator’s operation depends on the fact that an odd number of inversions exists around the loop.

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.

This is a voltage controller oscillator that was designed as a wide range oscillator to generate clock pulses for a stepper motor drive system. It does however have some interesting features. The original application used a stepper motor for its ability to operate over a very wide speed range, so this oscillator is also designed for a very wide frequency range. The prototype could be varied over 1,000,000:1 - six decades.

The V/F converter in Figure 1 is unique because it draws less than 30 µA from one unregulated supply while converting bipolar input voltages. It produces three CMOS-compatible, 0- to 10-kHz outputs: one (F+) that becomes active when the input voltage is positive, another (F­) that takes over for negative inputs, and a third (FABS) that produces a frequency proportional to the absolute value of the input.

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 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 Fig 1 generates a 50-Hz to 1-kHz sinusoidal waveform that exhibits lower than 60-dB THD. The input voltage controls the output frequency with the relationship 1 kHz/V. The output amplitude is invariant with frequency over the entire operating range. IC1 is a V/F converter with an input control range of 0 to 1V. You adjust R5 so that the output frequency equals 1 kHz with a 1V input.

This circuit is used to convert a mono audio signal into a stereo signal that can be panned between the left and right channel by a 0-10V control signal, it is intended for analog synthesizer systems. The circuit is mainly here for historical reasons, a higher quality panner may be built with the National Semiconductor LM13700 dual transconductance amplifier set up as a pair of voltage controlled amplifiers.

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.

This is a 0 - 6 MHz DDS VFO controlled by a PIC16F84 (or 'C84). The VFO is separated into two modules, the DDS module and the controller module. The PCB layout (double sided) for the DDS module is included as two Postscript files (scale 1:1). The .PS files can be copied to a Postscript capable printer such as HP LaserJet 4MP. Please note that the layout is mirrored to get the toner side of the film toward the PCB surface.

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.