Common RF receiving circuit design for toys (3 high-frequency parts)

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 capacitor three-point oscillator, and the oscillation frequency is consistent with the transmission frequency of the transmitter. The intermittent oscillation (also known as quenching oscillation) is generated during the oscillation process of the high-frequency oscillation, which in turn controls the oscillation and intermittence of the high-frequency oscillator. The frequency of the intermittent (quenching) oscillation is determined by the parameters of the circuit (generally 100 to several hundred kilohertz). If this frequency is selected low, the circuit has better anti-interference performance, but lower receiving sensitivity: conversely, if the frequency is selected high, the receiving sensitivity is better, but the anti-interference performance becomes worse. Both should be taken into account according to the actual situation.

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

When a control signal arrives, the circuit vibrates, the super noise is suppressed, and the high-frequency oscillator begins to oscillate. The speed of the oscillation process and the length of the interval 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 interval time of each oscillation is short, and the control voltage obtained is also high; conversely, when the amplitude of the received signal is small, the control voltage obtained is also low. In this way, a low-frequency voltage consistent with the control signal is obtained on the load of the circuit, and this voltage is another control voltage of the circuit state.