Voltage to Frequency

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).

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.

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.

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.

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No description available.

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 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.

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 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.