In our experiments, a lot of RF-Carriers need to be demodulated / mixed down into a Baseband. Up to now, our physicists used narrowband phase-shifters. But it was troublesome to synchronise two carriers in phase. And as we all know, phase differences (offsets from the 90°) cause degradation of the overall performance. We intended to propose a broadband solution without the hassle to adjust any phase-shift at all.

The Design is straightforward and impresses with simplicity. We use two D-Type Flip Flops, working as a Ring Counter. For high speed, ECL logic circuits have been used. They further offer two outputs which makes life even more easy. The Set and Reset input is not used and is therefore connected to gnd.

The limiter at the input mayst be left away, it is only necessary for student-proof designs.

This setup is also called Johnson Counter, Twisted Ring Counter or Modulo-4 Counter.

The board works nicely when a 10 dBm (10 mW) carrier is applied at the input. The used ECL D-Flip Flops work up to 3 GHz (says ON Semiconductor). The output frequency is always a fourth of th input frequency and should therefore go up to 750 MHz. The Device is powerd by + 5V and consumes up to 280 mA (600 MHz).

The output Jitter is below 1 ps, rms (says the Datasheet). Up to at least 2.5 GHz input.



First Test. Input is 20 MHz (SMC100A), +10 dBm. Output is 5 MHz, 500 mVpp




Lowpass filtered. Input is 600 MHz (SMC100A), +10 dBm. Output is 150 MHz


For mixing applications, a lowpass is not always necessary. Some mixers perform best, when using a square wave local oscillator.

The offered Gerber Files must not be used for commercial purposes. The ETH Quantumoptics as well as the Changpuak (white Elephant) Logo must stay intact when reproducing this board.

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