← Schematics & Diagrams

The Toolbox — Symbols

Block Diagram Elements

Standard block diagram symbols for RF system design — amplifiers, filters, mixers, converters, oscillators, and signal flow elements.

Amplifiers

A
AmplifierGeneral amplifier block. Triangle points in direction of signal flow. Gain expressed in dB.
LNA Low NF
Low Noise Amplifier (LNA)Amplifier optimized for minimum noise figure. Used at the front end of receivers to amplify weak signals without adding significant noise.
PA High Power
Power Amplifier (PA)High-power amplifier stage. Final stage in a transmitter chain. Efficiency and linearity are key parameters.
VGA Ctrl
Variable Gain AmplifierAmplifier with adjustable gain, often controlled by a voltage or digital input. Used in AGC circuits and signal conditioning.

Filters

LPF
Low Pass Filter (LPF)Passes frequencies below the cutoff frequency. Attenuates high frequencies. Used for anti-aliasing, harmonic rejection, and audio processing.
HPF
High Pass Filter (HPF)Passes frequencies above the cutoff frequency. Attenuates low frequencies. Used for DC blocking, noise reduction, and signal separation.
BPF
Band Pass Filter (BPF)Passes a range of frequencies between lower and upper cutoff frequencies. Used in receivers to select a desired channel while rejecting others.
BSF Notch
Band Stop / Notch FilterAttenuates a specific band of frequencies while passing all others. Used to reject interference at a specific frequency.

Mixers & Conversion

LO
MixerMultiplies two signals to produce sum and difference frequencies. Core component of superheterodyne receivers and frequency converters.
×N Freq Mult
Frequency MultiplierProduces an output signal at a multiple of the input frequency. Used to generate higher frequencies from a lower-frequency reference oscillator.
ADC ~ 101
ADCAnalog-to-Digital Converter. Converts a continuous analog signal to discrete digital values. Key parameter: sample rate and bit depth.
DAC 101 ~
DACDigital-to-Analog Converter. Converts discrete digital values to a continuous analog signal. Used in audio output and signal generation.

Oscillators & Timing

OscillatorGenerates a periodic signal at a specific frequency. Output frequency may be fixed or variable (VCO).
VCO Vtune
Voltage Controlled Oscillator (VCO)Oscillator whose frequency is controlled by an input voltage. Core component of PLLs and FM modulators.
PLL Phase Lock Loop
Phase Locked Loop (PLL)Feedback system that locks the phase/frequency of a VCO to a reference. Used for frequency synthesis, clock recovery, and demodulation.

Signal Flow

ATT −X dB
AttenuatorReduces signal power by a fixed amount expressed in dB. Used for impedance matching, level adjustment, and protecting sensitive inputs.
÷ −3 dB −3 dB
Splitter / CombinerDivides one signal into two equal outputs (splitter) or combines two signals into one (combiner). Each split causes 3 dB loss plus insertion loss.
Coupler −20 dB
Directional CouplerSamples a portion of RF power flowing in one direction. Used for power monitoring, SWR measurement, and signal injection.
①→② ②→③ ① ③ ②
CirculatorThree-port device that routes signals in one direction only — port 1→2, 2→3, 3→1. Used to isolate transmitter from receiver in duplexers.
LIM
LimiterClips signal amplitude above a threshold. Protects sensitive components from high signal levels. Also used to remove AM from FM signals.
MOD Data In
ModulatorImpresses information onto a carrier signal. Types include AM, FM, PM, ASK, FSK, PSK, and QAM depending on which carrier parameter is varied.
DEM Data Out
DemodulatorExtracts the information signal from a modulated carrier. The inverse of modulation — recovers the original baseband signal.