Pin
Name
Description
The transmitter RFoutput voltage is proportional to the input current to this pin. A series resistor is used to adjust
the peak transmitter output voltage. 0 dBm of output power requires about 450 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 ap-
pears to be a diode in series with a small resistor. Peak transmitter output power PO for a 3 Vdc supply voltage is
approximately:
8
TXMOD
P
O = 7*(ITXM)2, where PO is in mW, and the peak modulation current ITXM is in mA
5ꢀ resistor value is recommended. In the ASK mode (TR1100), this pin accepts analog modulation (shaped or
A
unshaped data pulses). ASK modulation is practical for data pulses 1 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 RLPF between this
pin and ground. The resistor value can range from 330 K to 820 ohms, providing a filter 3 dB bandwidth fLPF from
4.5 kHz to 1.8 MHz. The resistor value is determined by:
RLPF = 1445/ fLPF, where RLPF is in kilohms, and fLPF is in kHz
9
LPFADJ
A
5ꢀ resistor should be used to set the filter bandwidth. This will provide a 3 dB filter bandwidth between fLPF
and 1.3* fLPF 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.
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11
GND2
RREF
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.
1ꢀ resistor tolerance is recommended. It is important to keep the total capacitance between ground, Vcc and
A
this node to less than 5 pF to maintain current source stability. If THLD1 and/or THDL2 are connected 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
RTH2 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 50ꢀ-50ꢀ RF amplifier duty cycle. The value of the THLD2 resistor is given by:
12
THLD2
RTH2 = 1.67*V, where RTH2 is in kilohms and the threshold V is in mV
A 1ꢀ 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 RTH1 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:
R
TH1 = 1.11*V, where RTH1 is in kilohms and the threshold V is in mV
13
THLD1
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:
RTH1 = 2.22*V, where RTH1 is in kilohms and the threshold V is in mV
A 1ꢀ 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 tPRI is set by a resistor RPR between this pin and ground. The interval tPRI 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 RPR is given by:
RPR = 404* tPRI + 10.5, where tPRI is in µs, and RPR is in kilohms
A
5ꢀ resistor value is recommended. When the PWIDTH pin is connected to Vcc through a 1 M resistor, the RF
amplifiers operate at a nominal 50ꢀ-50ꢀ duty cycle, facilitating high data rate operation (TR1100). In this case,
the period tPRC 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 RPR is given by:
14
PRATE
RPR = 198* tPRC - 8.51, where tPRC is in µs and RPR is in kilohms
A
5ꢀ 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.
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RFM [ RF MONOLITHICS, INC ]
