AS3977-BQFT austriamicrosystems, AS3977-BQFT Datasheet - Page 17

• Manufacturer Part Number: AS3977-BQFT
• Description: IC RF TRANSMITTER FSK 16-QFN
• Manufacturer: austriamicrosystems

Specifications of AS3977-BQFT

• Frequency: 300MHz ~ 928MHz
• Applications: ISM
• Modulation Or Protocol: FSK
• Data Rate - Maximum: 100 kbps
• Power - Output: 10dBm
• Data Interface: PCB, Surface Mount
• Antenna Connector: PCB, Surface Mount
• Voltage - Supply: 2 V ~ 3.6 V
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-VQFN Exposed Pad, 16-HVQFN, 16-SQFN, 16-DHVQFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Features: -
• Memory Size: -
• Current - Transmitting: -

AS3977
Data Sheet - D e t a i l e d S y s t e m D e s c r i p t i o n
8 Detailed System Description
The AS3977 is based on a fully integrated sigma-delta controlled fractional-N synthesizer phase locked loop (PLL) and
a power amplifier (PA). A reference frequency generator including a crystal oscillator provides the comparison
frequency of the PLL and a high-precision clock output. A programmable Gaussian filter enables to minimize the
occupied bandwidth and adjacent channel power. A temperature sensor with digital read-out is included that allows
compensation of the crystal frequency drift due to temperature variation. An on-chip low drop out regulator (LDO) is
available in case an accurate output power independent of supply voltage variation is required. A second LDO for the
digital supply voltage helps to minimize interference between the analog and digital part and decreases the current
consumption of the digital part. A PROM enables the compensation of process variation. The AS3977 is controlled by
an external microcontroller via a bi-directional serial digital interface (SDI).
Reference Frequency Generator
The reference frequency generator consists of a crystal oscillator and frequency divider. The crystal oscillator can be
driven externally in case an external clock frequency is supplied.
Phase Locked Loop
The PLL is of standard charge pump type. The phase frequency detector is designed such that dead zone problems
are avoided. The charge pump current is programmable. All loop filter components are on-chip, the bandwidth is
programmable through the charge pump current. The differential based voltage controlled oscillator (VCO) has
integrated inductors and varactors. The VCO operates at a center frequency around 1.8GHz. To cover the specified
frequency range over process variation, the sufficiently wide overall tuning range is split into 16 overlapping frequency
bands. At start up of the PLL, an automatic range select circuit (ARS) selects the proper frequency band. The VCO
output frequency is divided by 2, 4, and 6, which enables to cover output frequencies in the range of 850 – 928 MHZ,
425 – 450 MHz and 300 – 320 MHz, respectively. A lock detector enables to monitor the PLL lock status.
Gaussian Filter and Digital Modulator
The programmable sigma-delta modulator controls the output frequency of the PLL. The order of the modulator is
programmable (MASH2 or MASH3). In combination with the programmable Gaussian filter for the data signal, the
modulator performs the FSK modulation with programmable deviation, whereby the Gaussian Filter enables to
minimize the occupied bandwidth and the adjacent channel power.
Power Amplifier
The power amplifier is single ended and consists of a preamplifier and an output stage, both with open collector. The
necessary external chokes can be connected to a LDO in case an accurate output power independent of supply
voltage variation is required. The output power is programmable up to 10dBm.
Temperature Sensor
The AS3977 includes a temperature sensor to measure the absolute temperature inside the chip. The analog value is
converted to a digital value and can then be read out by the microcontroller in order to control the output frequency
and/or the transmission power. The value of the chip temperature in degree can be obtained using following formula:
Temperature = TS < 9…0 > * 0.19 – 50
(EQ 1)
The temperature sensor can be used to compensate the crystal drift over temperature.
Note: AS3977 has the same temperature than the crystal only at start up and the temperature will increase immedi-
ately thereafter due to self heating.
Temperature sensor must be used only in the Clock Enable Mode as a stand alone block. It is mandatory to be used
with the PLL and Power Amplifier switched off.
Low Power Reset
The low power reset (LPR) disables the power amplifier, if the supply voltage falls below the low power threshold.
Low Drop Out Regulators
In order to avoid stability issues, external capacitors are required.
(see Table 1)
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Revision 3.5
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