Circuit arrangement for amplifying oscillator oscillations and converting same to rectangular signals

Claim 1

In a circuit arrangement for digitally indicating the frequency to which a radio receiver having both an AM tuning oscillator and an FM tuning oscillator is tuned, said circuit arrangement including means for coupling the output signals from said AM and FM oscillators to the input of a common broadband amplifier which has a bandwidth sufficiently broad so as to pass and amplify signal frequencies from both the AM and FM tuning oscillators and which converts the amplified output signals from said oscillators into rectangular signals, said coupling means sufficiently loosely coupling the output signals from said AM and said FM tuning oscillators to the common input of said broadband amplifier so that said tuning oscillators are not noticeably detuned by changes in capacitance of said broadband amplifier, and digital counting and indicating means for counting the frequency of said rectangular signals and for providing a digital indication of the frequency to which the particular tuning oscillator is tuned; the improvement wherein said common broadband amplifier comprises first and second inverters, each having a fast rise-time, which are each designed as an integrated circuit and which are connected in series with one another via a capacitance; and means for applying a respective bias voltage to the input of each of said inverters so that the operating point of each of said inverters lies on the steep portion of the curve indicating the relationship between the input voltage and the output voltage of the inverter, said means for applying a respective bias voltage including a resistive voltage divider connected from the output of said second inverter to a point of reference potential with said voltage divider having its tap connected with said input of said second inverter, which is connected behind said first inverter, to generate the biasing voltage for said second inverter.