This circuit will function accurately over a 10:1 frequency range from 1 kHz to 10 kHz, but will not respond as quickly as the basic wide range phase locked loop (PLL). The reason is the use of the CD4046 frequency detector. When a FIN edge occurs ahead of an F feedback pulse, pin 13 of the CD4046 pulls up on C1 via R1 = 1 kW. This current cannot be controlled or manipulated over as wide a range as “I1” in basic wide range phase locked loop (PLL). As a consequence, the response of this PLL is never as smooth nor fast-settling as the basic PLL, but it is still better behaved than most F-to-V converters. Show a picture schematic :
Q1 = 2N3565 OR 2N3904 HIGH BETA NPN
A1, A2, A3 = 1/4 LM324
ON CD4046, PINS 1, 2, 4, 6, 7, 10, 11, 12 ARE NO CONNECTION
USE STABLE, LOW-T.C. PARTS FOR COMPONENTS MARKED*
VS = +7 TO +15 VDC
As with the primary PLL, the detector feeds a current to integrated into C1 (and R2 provides the necessary “lead”). A1 merely acts as a buffer for the R1, C1 integrator. A3, optional, can provide a nicely filtered output. And A2 servos Q1, drawing a current out of C6 which is proportional to V2. Here the LM331 acts as a current-to-frequency converter and F output are precisely equivalent to the collector current of Q1. As with the primary like circuit, this PLL can be used as a quick and quiet F-to-V converter, or as a frequency multiplier. One of the most important uses of an F-to-V is to demodulate the frequency of a V-to-F converter, which may be situated at a high common-mode voltage, isolated by photoisolators, or to recover a telemetered signal. An F-to-V converter of this sort can provide good bandwidth for demodulating such a signal.