Peak Detector Timing
The Peak Detector attack time constant is set by the value of the ca-
pacitor at the PKDET pin. The attack time t
PKA
= C
PKD
/4167, where
t
PKA
is in µs and C
PKD
is in pF. The Peak Detector decay time con-
stant t
PKD
= 1000*t
PKA
.
Pulse Generator Timing
In the low data rate mode, the interval t
PRI
between the falling edge
of an ON pulse to the first RF amplifier and the rising edge of the
next ON pulse to the first RF amplifier is set by a resistor R
PR
be-
tween the PRATE pin and ground. The interval can be adjusted be-
tween 0.1 and 5 µs with a resistor in the range of 51 K to 2000 K.
The value of the R
PR
is given by:
R
PR
= 404* t
PRI
+ 10.5, where t
PRI
is in µs, and R
PR
is in kilohms
In the high data rate mode (selected at the PWIDTH pin) the re-
ceiver RF amplifiers operate at a nominal 50%-50% duty cycle. In
this case, the period t
PRC
from the start of an ON pulse to the first
RF amplifier to the start of the next ON pulse to the first RF amplifier
is controlled by the PRATE resistor over a range of 0.1 to 1.1 µs us-
ing a resistor of 11 K to 220 K. In this case R
PR
is given by:
R
PR
= 198* t
PRC
- 8.51, where t
PRC
is in µs and R
PR
is in kilohms
In the low data rate mode, the PWIDTH pin sets the width of the ON
pulse to the first RF amplifier t
PW1
with a resistor R
PW
to ground (the
ON pulse width to the second RF amplifier t
PW2
is set at 1.1 times
the pulse width to the first RF amplifier in the low data rate mode).
The ON pulse width t
PW1
can be adjusted between 0.55 and 1 µs
with a resistor value in the range of 200 K to 390 K. The value of
R
PW
is given by:
R
PW
= 404* t
PW1
- 18.6, where t
PW1
is in µs and R
PW
is in kilohms
However, when the PWIDTH pin is connected to Vcc through a 1 M
resistor, the RF amplifiers operate at a nominal 50%-50% duty cy-
cle, facilitating high data rate operation. In this case, the RF amplifi-
ers are controlled by the PRATE resistor as described above.
LPF Group Delay
The low-pass filter group delay is a function of the filter 3 dB band-
width, which is set by a resistor R
LPF
to ground at the LPFADJ pin.
The minimum 3 dB bandwidth f
LPF
= 1445/R
LPF
, where f
LPF
is in kHz,
and R
LPF
is in kilohms.
The maximum group delay t
FGD
= 1750/f
LPF
= 1.21*R
LPF
, where t
FGD
is in µs, f
LPF
in kHz, and R
LPF
in kilohms.
7
RFM [ RF MONOLITHICS, INC ]
