LV2700V Sanyo Semicon Device, LV2700V Datasheet - Page 7

• Manufacturer Part Number: LV2700V
• Description: Spread Spectrum Communications IC
• Manufacturer: Sanyo Semicon Device

Circuit Operation and Usage Notes
1. RF amplifier block
2. 236-MHz VCO
• The external 236-MHz VCO operates as follows in transmission and reception modes
• Main characteristics
3. FSK (FM) modulation technique
4. Notes on the FSK (FM) demodulated signal
— For half-duplex communication, a VCO circuit using a SAW resonator is used for both transmission and reception.
— For unidirectional communication, an LC circuit based VCO may be used for the transmission side.
— The reception PLL circuit lock time is between 2 and 10 ms when power is first applied and between 0.5 and 1.0
The LV2700V includes an on-chip RF amplifier that provides a gain of about 15 dB. An input sensitivity of about
–100 dBm can be acquired by adding an external 25-dB RF amplifier. Since IF frequency conversion is not used, a
costly IF filter is not required. While the frequencies used are selected to be values relatively infrequently used in the
weak field range (under 320 MHz), out of band components must be excluded using a bandpass filter after the
antenna to improve both the interference rejection characteristics and the input sensitivity.
[TX mode]
The VCO is adjusted to 236 MHz by a PLL circuit based on the 9.8304 reference.
That is, the phases of the VCO output that is input to pin 28 and the signal created by dividing the 9.8304 MHz
reference oscillator output by 24 are compared and edge-type phase detector. The error signal is integrated by the pin
22 loop filter and fed back through pin 26 to the VCO control input.
[RX mode]
The spread spectrum RF signal input to pin 3 is amplified by 15 dB and a narrow band signal is recovered by a
despreader circuit. The PLL circuit is then used for FM detection. That is, the phases of that signal and the VCO
output from pin 28 are compared, and the error signal is integrated by the pin 25 loop filter and fed back through pin
26 to the VCO control input. An FM detected demodulated signal can be acquired from pin 25 at this time.
Control sensitivity: 0.7 to 1.5 MHz/V
Frequency range: 236 MHz ±2 MHz
SAW resonator: We recommend the SAW resonators manufactured by Murata Mfg. Co., Ltd. (with a series
resonance frequency error of ±500 ppm).
See the VCO circuit on page 8 for the recommended circuit, which is a Colpitts oscillator circuit.
Modulation frequency range: 200 Hz to 150 kHz
When a modulated signal is applied to pin 22, there are limitations on low band FSK (FM) modulation, since this is
equivalent to applying the modulation as a disturbance signal to the PLL circuit. If it is necessary to apply modulation
to even lower bands, the 9.8 MHz reference oscillator circuit should be modified to be a VCXO circuit.
[For data input]
Apply the input data to pin 17. The signal is band limited to 300-kHz and then voltage limited to 1 Vp-p and output
from pin 18. This signal is passed through a series RC circuit and connected to pin 22. The capacitor is a DC-cut
capacitor of about 1 µF. The resistor should be about 20 kΩ, and is used for modulation adjustment.
[For analog signal input]
Do not use the internal 300-kHz low-pass filter and limiting amplifier, but rather apply the signal through the RC
circuit to pin 22 directly.
When the resistor is 20 kΩ, the optimal signal input level will be about 0.3 Vp-p.
[For data output]
Connect a capacitor of about 0.1 µF between pins 23 and 24, and another 1 µF capacitor between pin 10 and ground.
This will allow a CMOS-level data output signal to be acquired from pin 8.
[For analog output]
An analog signal can be acquired from pin 10. In this case, do not insert a capacitor between pin 10 and ground. The
cutoff frequency of the internal 150-kHz low-pass filter is set somewhat high for two reasons: to prevent PN code
leakage and to limit attenuation of high-speed data as much as possible. As a result, this filter is inadequate for
ms after a transition from no input to the input present state.
LV2700V
No. 5651-7/9