FX205 Tone Encoder

Tone Encoder in Signalling System

FX105 CML Tone Decoder


  • Pseudo-Sinewave Output
  • Choice of Package Styles
  • Wide Frequency Range Frequency Range
Pseudo-Sinewave Output
Choice of Package Styles
Wide Frequency Range
  • Adjustable Output Amplitude
  • Optional Timed Tone Bursts
  • Converts External Input Pulses to Sine Wave Output
  • Hermetically Sealed Me
  • tal can Package


The FX205 and FX205P are monolithic pseudo-sinewave generators. The FX205 is encapsulated in a hermetically sealed metal can, and the FX205P is packaged in a plastic DIL.

The circuits have an extensive range of applications encompassing telecommunications, control systems and alarm or supervisory signalling.

The output tone frequency is adjustable between 30 Hz and 5 kHz using an external resistor and capacitor (R1 and C1). Figures 4 and 5 show the component value of R1 for given values of C1 required to generate any frequency in the range. R2 is fixed at ten kohms.

The output frequency, f0, can be obtained from


f─────────── Hertz


Where R1 and R2 are expressed in megaohm, C1 is in microfarad, and the value 5.6 is a constant of the device and is subject to a tolerance of ±10%.

The output frequency can range from DC to 50 kHz by providing external clock pulses to the R1C1 pin. The input clock must be eight times the required output frequency.

The FX205 and FX205P will generate an output for the period that the Enable Gate input is held positive. Optionally, a resistor (Rt) and capacitor (Ct) can be provided.

This ensures that the output is generated for a minimum duration given by

T = 0.7 Rt Ct seconds

where Rt is expressed in megaohm, Ct is in microfarad, and 0.7 is a device constant (tolerance ±5%).

The monostable is not re-triggerable, and a further timed period can only be initiated after completion of the original burst. Should the Enable input be held positive for longer than time T, the device will continue generating a tone until disabled.

The output is generated in the form of sinusoidal weighted current steps. Multiple tones can be mixed by connecting outputs to a common load resistor. The circuit is designed to always start and end tone generation at the minimum current step (i.e. most negative output voltage as shown in Fig.3).

The output voltage can be adjusted over a range of ±35% from the nominal level by applying a voltage (Vb) to the Amplitude Control input. Vb can range from 25% to 55% of the supply voltage (internal bias is 40% nominally).

FX205 CML Pin Configuration

Pin Configuration

FX205 CML Components


FX205 CML Functional schematics

Functional Schematics