Circuit Description

 

Circuit Description

The circuit diagram for the CMOS Transmitter can be seen in the following figure. Power to the circuit is derived via B1, which is a 9 volt battery. A pair of 4011 NAND gate stages, U1c and U1d, are configured like a radio-frequency (RF) oscillator (carrier). The remaining a couple of CMOS gates, U1a and U1b, are utilized to build an audio frequency (AF) oscillator (modulator).

Switch S1 helps activating an deactivating the modulation process to enable the exchange of an complex information with the Transmitter. Once the switch S1 is pressed, the AF oscillator using U1a, U1b, R4, and C1, begins producing an acoustic signal. This signal switches ON and OFF the CMOS gates U1c, U1d, R2, R3, and C2. included in the the RF oscillator stages.

During the ON periods, the RF oscillator operates at 1 MHz frequency. This frequency output is delivered out to the ANT1 as an AM signal.

In the switched ON position, the RF oscillator operates at 1 MHz. The frequeny output is delivered to ANT1 in the form of AM signal. Remember that apart from R3, the AF and RF circuits are organized exactly in an identical manner. The function of R3 is to cause tuning to the Rf oscillator.

As soon as the momentary-contact, pushbutton S1 is pressed and released, the AF oscillator is switched off. Resistor R1 causes the voltage at pin 2 of UIa to become low deactivating the circuit. When you press S1 again, pin 2 turns high. This allows the circuit to yet again begin flicking across its a couple of stable states.

The first of these states is the condition where the U1a output remains high and the U1b output is rendered low. The second state is that condition where the U1a output turns low and the U1b output turns high.

The function of capacitor C1 in this CMOS transmitter circuit is to regulate the speed at which the changeover happens between the two states. If the capacitor hadn't been used, would have caused the circuit to oscillate at an abnormal, and incredibly fast rate. This would have also caused the frequency to get unstable due to varying room temperature, the wire dimensions that join the circuit with each other, and even with the proximity of your body part to the IC.

This is exactly how C1 handles the frequency of the flipping states: As soon as U1a flips and attempts to switch the circuit through the 1st state to the second state, C1 holds the circuit within the first state for a short time, by doing so helps to reduce the frequency. The capacitor is able to do this since it is coupled to the input of U1a, in the same way as R4 is.

So long as C1 is in the charged up condition, it is able to "overpower" resistor R4, stopping it from modifying the U1a input. Now, as C1 begins losing charge by means of R4, this permits U1a to topple over to the second state.