The ZIF portion of DZIF refers to “Zero Intermediate Frequency” and it is just my favorite abbreviation for homodyne or synchrodyne. They all mean the same and are technologies that evolved in parallel with the superheterodyne around the 1920-1930 period. The “D” part of DZIF refers to double conversion meaning that a high IF is used in addition to the ZIF.
In the hobby industry, the double conversion receiver had become standard and the usual design employed a 10.7 MHz FIRST IF and 455 KHz SECOND IF and the modulation most times was PPM FM. This design(S) evolved from about 1980 up to and beyond 2000. From a mechanical damage standpoint the 455 KHz transformers were the weak link. Also there were design missteps in gain distribution between the FIRST IF and the 455 KHz second IF.
During this period first Siemens, then Signetics and finally Philips developed a line of ICs specific to the cellular phone industry. Very specifically they had such chips as the ‘612 which provided a balanced mixer with internal oscillator. Another chip was the ‘614 which when combined with the ‘612 had capability of dual conversion and produced an RSSI indication of Received Signal Strength Indication
Internal to the output end of the ‘614 was an FM demodulator that was driven by a limited IF signal, coupled to an external LC tuned to 455KHz and with a Q=20, providing an FM discriminator with peak-to-peak separation of approximately 25KHz and good linearity. This addressed the needs of the cellular phone needs at that time nicely.
Being aware of ILOD and also ZIF ideas it occurred to me you could combine the two ideas and with relatively minor reconnection produces a DZIF. The change at the end of the ‘614 was to remove the so-called quadrature coil and replaced it with an ILOD tank circuit driven at 10.7 MHz using the oscillator section of a second ‘612. See the included schematic/block diagram.
The ‘614 now operated at 10.7MHz which it can nicely and the second IF is now ZERO or ZIF. This then feeds to an LPF 3-4 pole filter that is just “r” and “c” and not only small but extremely rugged. Of course because the second IF was “zero” (ZIF), no 455 KHz transformer or Clevite type filters were needed—hence a space saving plus more rugged.
All good things.
In order to be meaningful, I would have thought that the term "Zero IF" would need to refer to performing the demodulation itself at baseband. Such demodulation requires that two mixed signals are available at baseband - the so-called InPhase and Quadrature components.
This system of course carries out the demodulation at the 10.7-MHz IF.
This is of course no criticism of the technique itself - merely that the definition used here for "Zero IF" would cause nearly every FM demodulation system I have either designed or tinkered to be redefined as being a hybrid ZIF (or DZIF).
Posted by: George Storm | April 24, 2012 at 11:58 AM
The '614 with '612 is a single conversion receiver. The '615 with '612 is a double conversion receiver. Many years ago I was given a NE604 (forerunner of the '614) pre-production sample for evaluation.
Posted by: Victor Koren | April 24, 2012 at 04:11 PM
DZIF response----The oscillator of the ILOD IS the second oscillator. Recall the rational of the dual conversion receiver what the FIRST IF (10.7 MHz) solved the image problem while the SECOND IF @ 455 KHz solved the adjacent channel selectivity problem. In DZIF the second oscillator is at 10.7 MHz so that adjacent channel interference, either above or below can be handled by a LPF, Low Pass Filter. So in DZIF the 455 KHz function is now handled at baseband. The mixer for the second conversion is the phase detector part of ILOD. IT WORKS.
BTW Victor you are correct about the '614 vs '615. That is why I used the '614.
Posted by: Carl Schwab | April 25, 2012 at 10:36 AM