WEN H. KO 
1139 
Table II. — Performance of K-5 and K-6 Transmitters 
Item K-5 K-6 Hybrid 
Size, less battery 0.8 cm diam. X 0.2 cm 0.9 X 0.6 X 0.2 cm 
Weight, less battery 0.44 gm 0.6 gm 
Power Consumption... 0.2 volt, 1.2 mA 1.3 volt, 0.5 mA 
RF Frequency 100—250 MHz 100—250 MHz 
System Noise 
(10 kO, 1 kHz) 3 ixV 3 5 /iV 
Dynamic Range 
(limited by 
receiver 10^ . . . 10'' 
Frequency Response... 0.1 — 20 kHz 0.1 — 20 kHz 
Input Impedance 300 kfi to several Mfi- 300 kfl to several Mfl 
Transmission Range... 5 /tV at 1 to 2 m 5 ixV at 1 to 2 m 
Carrier Frequency 
Temperature 
Stability- Better than 0.05%°C..- Better than 0.05%°C 
is estimated to be between 10 to 20 mw/cm^. 
The RF power received by a 1 cm radius spheri- 
cal power detector is about 2 mW. 
The K-5 and K-6 transmitters were im- 
planted in mice, rats, rabbits, dogs and monkeys 
to transmit EMG and EGG with platinum elec- 
trodes. Packages with a replaceable battery, 
rechargeable battery, and RF power detector 
with or without reed switch were fabricated in 
lots of 50 to 100 units. Reliability data were ob- 
tained on these lots. 
In order to reduce the overall size and weight, 
the power consumption of the transmitter 
should be minimized. With the new micropower 
transistors and design techniques, the power 
consumption can be greatly reduced. For exam- 
ple, the circuit shown in Figure 2(b) was re- 
designed 1* to provide a very low duty cycle of 
10-4 to 10-5. Tj^g M-3/K-6F single channel 
PFM transmitter consumes about 1 jitW power 
and can be used for low frequency band signal 
such as temperature or pressure. A package us- 
ing a #312 battery can operate continuously for 
over 6 months. The performance of the M-3/ 
K-6P unit is given in Table III. 
Table III. — Performance of M-3/K-6P Unit 
Over -all size, including battery 
(M-3 plus K-6) 
Weight of epoxy coated package 
(including #312 battery) 
RF frequency 
Power supply voltage 
Battery current drain 
Operating temperature range. 
On time of pulses 
Duty cycle _ 
[20 X 12 X 5 mm] X 2 
5 gm 
.- 120 MHz (others as specified) 
... 1.3 or 2.6 volts 
._ 0.5 50 fiA 
... 20°— 45° C (others as specified) 
.. 10 200 ,asec 
... 10-* 10-5 
A single channel PFM micropower transmit- 
ter with high input impedance amplifier was 
also designed. ^5 The block diagram and per- 
formance of this transmitter are given in Fig- 
ure 4 and Table IV, respectively. For long term 
monitoring, in order to improve the base line 
stability, a subcarrier is needed even for single 
channel transmission. This is similar to the 
multiple channel transmitters where subcarriers 
are used to separate the channels transmitting 
over the same RF frequency. For those fre- 
quency division multiplex systems, the sub- 
carriers have different frequencies; the signal 
may use an AM or FM scheme to modulate the 
subcarrier. Both AM/FM and FM/FM multi- 
plex systems with 4 to 8 channels '^^•'^'^ have been 
reported. 
In the time division multiplex system, the 
signal channels are sampled and transmitted at 
different time slots. PAM/FM and PDM/PAM 
systems were designed at Case Western Reserve 
University ^^'^^ and the modular blocks were in- 
tegrated into chips or flat packs. Depending on 
the signal frequency band, these systems cover 
2 to 30 channels. 
Receiving Systems 
Due to restrictions on size and weight, im- 
plant telemetry transmitters are generally de- 
signed with minimum components required at 
low power level or operating in low duty cycle 
pulse mode. Therefore, noise and interference 
become serious problems at the receiving end. 
The transmitting frequency is generally not sta- 
bilized and drifts with time and motion of the 
subject due to change of loading. In order to 
maintain system reliability and performance, 
the receiver and demodulator should incorporate 
various noise discriminating schemes such as 
(a) Automatic Gain Control (AGC) for fading; 
(b) Automatic Frequency Control (AFC) and 
phase locked loop for frequency drift; and (c) 
noise limiter or amplitude discrimination for 
noise and interference. 
For pulse modulated signal, the interference 
problem is especially serious. At Case Western 
Reserve University, pulse amplitude discrimi- 
nation, pulse width discrimination and pulse 
frequency discrimination methods have been 
