Pin
Name
Description
The transmitter RF output voltage is proportional to the input current to this pin. A series resistor is used to adjust
the peak transmitter output voltage. 0 dBm output power requires about 250 µA of input current. In the ASK mode,
minimum output power occurs when the modulation driver sinks about 10 µA of current from this pin. In the OOK
mode, input signals less than 220 mV completely turn the transmitter oscillator off. Internally, this pin appears to
be a diode in series with a small resistor. Peak transmitter output power P
O
for a 3 Vdc supply voltage is approxi-
mately:
P
O
= 16*(I
TXM
)
2
, where P
O
is in mW, and the peak modulation current I
TXM
is in mA
A ±5% resistor value is recommended. In the OOK mode, this pin is usually driven with a logic-level data input
(unshaped data pulses). OOK modulation is practical for data pulses of 30 µs or longer. In the ASK mode, this pin
accepts analog modulation (shaped or unshaped data pulses). ASK modulation is practical for data pulses 8.7 µs
or longer.
The resistor driving this pin must be low in the receive and power-down (sleep) modes.
Please refer to
the
ASH Transceiver Designer’s Guide
for additional information on modulation techniques.
This pin is the receiver low-pass filter bandwidth adjust. The filter bandwidth is set by a resistor R
LPF
between this
pin and ground. The resistor value can range from 330 K to 820 ohms, providing a filter 3 dB bandwidth f
LPF
from
4.5 kHz to 1.8 MHz. The resistor value is determined by:
8
TXMOD
9
LPFADJ
R
LPF
= 1445/ f
LPF
, where R
LPF
is in kilohms, and f
LPF
is in kHz
A ±5% resistor should be used to set the filter bandwidth. This will provide a 3 dB filter bandwidth between f
LPF
and 1.3* f
LPF
with variations in supply voltage, temperature, etc. The filter provides a three-pole, 0.05 degree
equiripple phase response. The peak drive current available from RXDATA increases in proportion to the filter
bandwidth setting.
GND2 is an IC ground pin. It should be connected to GND1 by a short, low inductance trace.
RREF is the external reference resistor pin. A 100 K reference resistor is connected between this pin and ground.
A ±1% resistor tolerance is recommended. It is important to keep the total capacitance between ground, Vcc and
this node to less than 5 pF to maintain current source stability. If THLD1 and/or THDL2 are con nected to RREF
through resistor values less that 1.5 K, their node capacitance must be added to the RREF node capacitance and
the total should not exceed 5 pF.
THLD2 is the “dB-below-peak” data slicer (DS2) threshold adjust pin. The threshold is set by a 0 to 200 K resistor
R
TH2
between this pin and RREF. Increasing the value of the resistor decreases the threshold below the peak de-
tector value (increases difference) from 0 to 120 mV. For most applications, this threshold should be set at 6 dB
below peak, or 60 mV for a 50%-50% RF amplifier duty cycle. The value of the THLD2 resistor is given by:
R
TH2
= 1.67*V, where R
TH2
is in kilohms and the threshold V is in mV
A ±1% resistor tolerance is recommended for the THLD2 resistor. Leaving the THLD2 pin open disables the
dB-below-peak data slicer operation.
The THLD1 pin sets the threshold for the standard data slicer (DS1) through a resistor R
TH1
to RREF. The thresh-
old is increased by increasing the resistor value. Connecting this pin directly to RREF provides zero threshold.
The value of the resistor depends on whether THLD2 is used. For the case that THLD2 is not used, the accept-
able range for the resistor is 0 to 100 K, providing a THLD1 range of 0 to 90 mV. The resistor value is given by:
10
GND2
11
RREF
12
THLD2
13
THLD1
R
TH1
= 1.11*V, where R
TH1
is in kilohms and the threshold V is in mV
For the case that THLD2 is used, the acceptable range for the THLD1 resistor is 0 to 200 K, again providing a
THLD1 range of 0 to 90 mV. The resistor value is given by:
R
TH1
= 2.22*V, where R
TH1
is in kilohms and the threshold V is in mV
A ±1% resistor tolerance is recommended for the THLD1 resistor. Note that a non-zero DS1 threshold is required
for proper AGC operation.
The interval 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 t
PRI
is set by a resistor R
PR
between this pin and ground. The interval t
PRI
can be ad-
justed between 0.1 and 5 µs with a resistor in the range of 51 K to 2000 K. The value of R
PR
is given by:
R
PR
= 404* t
PRI
+ 10.5, where t
PRI
is in µs, and R
PR
is in kilohms
A ±5% resistor value is recommended. When the PWIDTH pin is connected to Vcc through a 1 M resistor, the RF
amplifiers operate at a nominal 50%-50% duty cycle, facilitating high data rate operation. In this case, the period
t
PRC
from start-to-start of ON pulses to the first RF amplifier is controlled by the PRATE resistor over a range of 0.1
to 1.1 µs using a resistor of 11 K to 220 K. In this case the value of R
PR
is given by:
R
PR
= 198* t
PRC
- 8.51, where t
PRC
is in µs and R
PR
is in kilohms
A ±5% resistor value should also be used in this case. Please refer to the
ASH Transceiver Designer’s Guide
for
additional amplifier duty cycle information. It is important to keep the total capacitance between ground, Vcc and
this pin to less than 5 pF to maintain stability.
14
PRATE
10
RFM [ RF MONOLITHICS, INC ]
