Quote:
Originally Posted by Radio Wrangler
There were bipolar mixers, but not high dynamic range ones... I'mnot sure when the SL6440 was released, but it was a lower frequency part really.
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I think one of the first well-known bipolar integrated doubly balanced mixers based upon the six-transistor Gilbert cell was the Motorola MC1496. I cannot pinpoint when it was introduced, but I’d guess around 1968-69. Plessey had a broadly similar device, the SL640C, which probably arrived soon after the MC1496.
The MC1496 seemed to be usable both at the back end of signal-chain, for example as an SSB demodulator, and towards the front end, as a mixer, at least in situations where it was appropriate for the signal levels and bandwidths encountered. The previously mentioned Sansui TU-X1 “supertuner” used a 1496 as mixer on the AM side, and the Marconi Apollo marine HF receiver used an SL640C as first mixer. Even earlier in using a Gilbert cell for demodulation was the Sprague ULN2111 FM IF sub-system of 1967, which combined a limiting amplifier with a quadrature demodulator. It was quickly followed by a whole host of similar devices, many aimed mostly at TV FM sound. Motorola had previously used what was effectively a Gilbert cell for the 1st, agc’d stage of its MC1350 TV IF amplifier block, and then again in 1969 for its MC1330 TV quasi-synchronous demodulator, which spawned a whole raft of functionally similar and progressively more complex ICs. In fact it might be said that the bipolar mixer form was pivotal in establishing the use of ICs for consumer equipment, and this was happening concurrently with the introduction of fets for the very front end work. With ICs, whilst the FM tuner makers were comfortable in the early days with using building block ICs such as the µA703 and CA3028, each IC typically replacing one transistor, apparently this was resisted by the mass-producers, particularly in respect of TV receivers. Motorola’s MC1350, which replaced the first two regular IF stages (with the MC1330 replacing the third and the diode demodulator) followed the MC1550, which functioned as a single IF stage, but which evidently was not accepted by the industry. And the MC1350 was very quickly segued into the MC1352, which added a gated agc circuit to increase functionality. Motorola was also early with an IC colour TV subcarrier demodulator based upon bipolar multipliers, whereas RCA had been proposing dual-gate mosfets for this role. Here I think the IC approach won decisively and quickly.
Getting back to the theme of what was not done or seldom done, finding an example of an essentially consumer-level item that used a high current bipolar feedback RF amplifier might be difficult, whereas DBMs can be found here and there.
Cheers,