Pulse frequency detector

Claim 1

Apparatus for producing an output in accordance with the repetition frequency of a plurality of pulses, said apparatus comprising: a first capacitor; first means for impressing voltage pulses across said first capacitor; a second capacitor; a switch connected between said capacitors; second means to close said switch periodically; said first means including a first monostable multivibrator responsive to the leading edges of input pulses thereto, one side of each capacitor being connected to a point of reference potential, a first resistor connected from said first multivibrator to the other side of said first capacitor, said switch including a first junction type, fieldeffect transistor having a source, a drain, and a gate, said first transistor source being connected to the other side of said first transistor, said second means including a second monostable multivibrator adapted to turn said switch on over an initial portion of the period that said first multivibrator tends to charge said first capacitor, a second resistor connected in parallel with said second capacitor, second and third junction type, field-effect transistors each having a source, a drain, and a gate, said second and third transistors being connected as source followers, third and fourth resistors connected from the sources of said second and third transistors, respectively, a third capacitor connected in parallel with said third resistor, means to supply a constant bias to said third transistor gate, the other side of said second capacitor being connected to said second transistor gate, a single-pole multiple-throw switch, a contact for each throw, a variable resistor connected from each contact to the source of one of said second and third transistors, and an electric current meter connected from the pole of said single-pole switch to the source of the other of said second and third transistors.