Using the HT45F4630 RF Function

AN0422E V1.00 1 / 4 April 12, 2016

Using the HT45F4630 RF Function

D/N: AN0422E

Introduction An RF function can be implemented using a Timer and the internal circuits of the

HT45F4630 together with some external circuitry. For the transmitter, the Timer

continuously outputs PWM signals with a frequency fixed at 125 kHz. The receiver is

composed of an external envelope detection circuit and an internal amplifier circuit in the

device.

Functional Description The red box below shows the RF transmitter PWM output with a frequency of 125kHz.

High Voltage Driver Block Diagram

The RF receiver circuit is shown below. The dashed part shows external circuitry while

the solid line shows the device internal circuits.

Schmitt Trigger

Wave Shaping

Signal

Amplifier

Envelope

Detector

Using the HT45F4630 RF Function

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Operating Principles

C2

ua(t)uΩ(t)

D

C1 C RLL1 RS

Fig.1 Envelope Detector Schematic Circuit

Fig.1 shows a typical envelope detection circuit. The amplitude-modulated signal ua(t),

which comes from an intermediate or high frequency amplifier, is supplied to the L1C1

loop circuit. After detection a voltage uΩ(t) will be generated on the load RLC, with the

voltage changing according to the ua(t) envelope as shown in Fig.2. The detector output

uΩ(t) has a proportional relationship with the peak of input signal ua(t), therefore it is also

called a peak detector.

Diagonal Clipping Distortion

t

ua(t)uΩ(t)u

t2t1 t3 Fig.2 Output and Input Voltage Waveforms of Envelope Detector

Fig.2 shows the operating principles of an envelope detector. For t1<t<t2, if the input

signal instantaneous value, ua(t), is greater than the output voltage, uΩ(t), then the diode

will be conducting and the capacitor C will charge via the diode forward resistance, ri，and

uΩ(t) increases, For t2<t<t3, where ua(t) is less than uΩ(t), the diode is cut-off and the

capacitor will be discharged via RL, and therefore uΩ(t) decreases. The diode will conduct

again when t is equal or greater than t3. The process above is then repeated. The output

voltage, uΩ(t), therefore has a corresponding relationship with the input signal envelope,

and will be generated if an appropriate time constant, RLC, is selected. If the time

constant is too large, the discharge rate will be reduced and uΩ(t) may remain always

greater than ua(t) when the input signal envelope decreases, thus resulting in the diagonal

clipping distortion, as shown in Fig.2. Additionally, the detector output is usually coupled

to the next stage amplifier using a capacitor and resistor circuit, as shown in the dashed

part of Fig.1. If Rg is too small, the bottom of the detected output voltage uΩ(t) will be cut,

i.e. bottom clipping distortion occurs.

Using the HT45F4630 RF Function

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Demo Board Circuit

Conclusion This application note has shown the RF function operating principles and usage for the

HT45F4630. A program example is also provided to help users understand how to use

the HT45F4630.

Program Example This program takes the H-Bridge direct drive after a correct read operation of the RF as

an example.

RF.zip

Versions and Modify Information

Date Author Issue

2016.02.24 王子齊 First Version

Reference Files

Reference file：HT45F4630 Data Sheet

For more information, refer to the Holtek’s website www.holtek.com.

Using the HT45F4630 RF Function

AN0422E V1.00 4 / 4 April 12, 2016

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