I wrote about this in April last year where I also mentioned that the 1 Volt design from 2000 later had been corrected. Those corrections can be found in the article in QRP-Report 3/2011: "Niederspannungs-Schaltungstechnik - der 1-V- und der 2-V-transceiver" (Low voltage circuit technology - the 1 Volt and the 2 Volt transceivers). The improvements are concerned with better input filtering at 14 MHz with a quartz crystal in the front-end filter and better efficiency in the mixer and removal of an audio stage in the direct conversion receiver. This design only uses bipolar transistors and no ICs.
This is different in the newer 2 or 3 Volt transceiver for 7 MHz. Here an impressive figure of only 5 mA power consumption for the receiver is achieved. The transmitter consumes about 250 mA. Several MC1496P balanced modulator/demodulator ICs are used for the mixers in the transmitter and the superhet receiver, and for the product detector of the receiver. They seem to run quite comfortably on only 1.8 Volts as supplied by a low-droput regulator from the battery supply. The TDA7050 is used for the audio output stage. This is a low voltage audio amplifier for headphones which can operate with a supply voltage down to 1.6 V.
The design is said to benefit from low voltage technology of mobile phones. This is the case for circuitry like that of the output stage of the transmitter which consists of a pair of BFG21W transistors. However, both of the ICs have been around for many years.
I think this was a very inspiring read, and the final comment about power consumption from the second article is interesting. They say that with two AA-batteries, the receiver will last for 285 hours, which is the same as 70 days of listening of 4 hours per day. With transmission for 10% of the time, the set of batteries will last for 4 weeks!
- Related post: Whatever happened to the 1 Volt QRP Transceivers?