Commonly used RF receiving circuits for toys (2)

Super regenerative detection receiver: The super regenerative detection circuit is actually a high-frequency oscillator controlled by intermittent oscillation. This high-frequency oscillator uses a capacitive three-point oscillator, and the oscillation frequency is consistent with the transmitter's transmission frequency. The intermittent oscillation (also known as quenching and decoration oscillation) is generated during the oscillation process of high-frequency oscillation, which in turn controls the oscillation and intermittence of the high-frequency oscillator. The frequency of intermittent (quenching) oscillation is determined by the parameters of the circuit (generally 100 to several hundred kilohertz). If this frequency is selected low, the anti-interference performance of the circuit is better, but the receiving sensitivity is lower; on the contrary, if the frequency is selected high, the receiving sensitivity is better, but the anti-interference performance becomes worse. Both should be considered based on the actual situation.

The super regenerative detection circuit has a very high gain. When no control signal is received, due to interference from external stray signals and the thermal shock of the circuit itself, a unique noise is produced, called super noise. The frequency range of this noise It is between 0.3~5kHz and sounds like a "rustling" sound like running water. When there is no signal, the super-noise level is very high, and the noise voltage is output after filtering and amplification. This voltage is used as a control signal for a state of the circuit, making the relay close or open (depending on the designed state).

When a control signal arrives, the circuit vibrates, the super noise is suppressed, and the high-frequency oscillator begins to oscillate. The speed at which the oscillation process is established and the length of the intermittent time are controlled by the amplitude of the received signal. When the amplitude of the received signal is large, the starting level is high, the oscillation process is established quickly, the intermittent time of each oscillation is short, and the obtained control voltage is also high; conversely, when the amplitude of the received signal is small, the obtained control voltage is also low. In this way, a low-frequency voltage consistent with the control signal is obtained on the load of the circuit. This voltage is another control voltage for the circuit state.