RS-GGO10-O2x GPS Guided Oscillator, OCXO, with or without GPS receiver

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1 RS-GGO10-O2x GPS Guided Oscillator, OCXO, with or without GPS receiver The RS GGO10 O2x is a 10MHz reference oscillator with almost the same form factor as standard OCXO's (28x25.8mm) with slightly increased width and height. A combination of novel circuits, special firmware and algorithms enable us to build this high performance unit in an ultra miniature size. The RS GGO10 O2x is based on the same refined technology which enabled our successful RS GGOxx T (TCXO based). As it uses an oven controlled crystal oscillator it will take some minutes 25C) to achieve the desired full GPS lock. After the warm up time of the OCXO 25C) the lock is established and as longer the RS GGO10 O2x is receiving the 1PPS signal as more accurate it will get. It is also highly recommended to keep the RS GGO10 O2x permanently powered to achieve the best results. Forget to search for a Rubidium standard to recalibrate your reference on a regular basis! Hook it up to a GPS and you have the best possible accuracy and stability short of a Rubidium standard. The RS GGOxx are true disciplined crystal oscillator and as such they provide extremely low phase noise with no phase discontinuity or jumps or spurious as can be observed with other solutions! Phase noise is NOT impacted during frequency correction either. As the GPS signal is NIST traceable all RF SUISSE frequency references with GPS guidance are NIST traceable too and as such do not need calibration. As long as a GPS signal is applied they act as secondary standards. Via a 2 wire interface which operates identical to the well known I 2 C the estimated accuracy can be read from the RS GGO10 O2x. However, programming is only an option but not required for normal operation. As an alternative the same pins can be used to drive a duo LED to indicate the internal status (IND = L). Red = no GPS signal, Amber = locking, Green = locked. This type of oscillator is commonly called a GPS disciplined oscillator. The word disciplined is misleading as the crystal actually has a better discipline or short term stability then the GPS 1PPS signal. The 1PPS signal is only accurate if it is integrated over a larger time frame. During the design of the circuit it was found that just locking the crystal oscillator to the 1PPS signal with a PLL can lead to undesired offsets (jitter) in frequency which isn't what one expects from a precision reference but what is commonly found in other designs. There is just no good loop bandwidth compromise between responsiveness and speed and suppression of jitter and false or missing pulses. A PLL, no matter whether it is made with PLL ICs or implemented in a DSP, makes for a long time to achieve a precision lock and it will not enable the calculation of the current accuracy and measurement of the GPS jitter. This is why a different locking mechanism with several special algorithms was developed which make sure that the unavoidable and unpredictable jitter of the 1PPS signal will not have a negative effect on the short nor the long term stability of the system. Missing GPS pulses or total failure of the GPS signal will not lead to instant offsets in frequency or immediate loss of accuracy. In its tiny package it contains a high quality OCXO and all the electronics to lock to the 1PPS pulse, things which are usually seen on large boards with less capability and still called tiny. In short, the GPS signal really guides the OCXO onto the correct frequency which is why we finally settled to call it a GPS Guided Oscillator (GGO). The RS GGO10 O2x, once hooked up to a GPS antenna and within a certain accuracy, will measure the jitter of the GPS and use the results to optimize it's acquisition and control routines. This allows the combination of various commercially available GPS puck antennas with it. Active antennas are preferred. However, it has to be stressed that the GPS antenna should be installed with a large unobstructed view of the sky to get the best possible reception! The power noise generated by the integrated GPS receiver will make the RS GGO10 O2G slightly less stable than the 1PPS input model RS GGO10 O2P. If the very best stability is required the use of the RS GGO10 O2P is recommended and a GPS module can be installed under the unit. Page 1 of 11

2 Block diagram ( O2G): Functional description: The basic function of the RS GGOxx O2x is to phase lock the crystal oscillator to a GPS 1PPS signal. It accurately measures the phase difference between the 1PPS signal and the oscillator which is then passed through a Kalman filter to remove the phase jitter of the 1PPS signal. The Kalman filter also collects information about the state of the oscillator, estimates the actual frequency offset of the crystal oscillator and the phase jitter of the 1PPS signal. At the same time it provides information about the actual accuracy of the measurements. All this information is used to determine the best possible correction signal. A high resolution DAC is used to apply the correction signal to the tuning input of the crystal oscillator. To prevent sudden changes the DAC output passes through a low corner frequency lowpass filter. The information provided by the Kalman filter can be queried via IIC bus or can be used to drive a Status indicator LED. To achieve the best possible accuracy in combination with a fast lock time, the RS GGOxx will adapt the effective filter bandwidth based on the gathered informations. It will start with a large filter bandwidth and will reduce the bandwidth as longer it receives a valid 1PPS signal. Additional firmware modules prevent that the RS GGOxx O2x reacts to missing or false pulses and prevents that the oscillator makes sudden changes based on wrong 1PPS inputs. These could be caused by missing GPS signal, or erroneous outputs from the GPS receiver. In case the 1PPS stream gets unstable or missing the RS GGOxx O2x remains on the last known good position and is as stable as its crystal oscillator. As longer the pulses are missing as wider it opens the loop and once the signal is stable again it re locks the oscillator. For short interrupts there will be no detectable change in frequency as the RS GGOxx first monitors the incoming signal to ensure a smooth lock. Note: As the GPS control circuit has to improve the stability of the OCXO by a factor of ~1000 rapid changes in temperature might be able to offset the frequency to the point where the loop has to coarse capture the signal again leading to amber LED's. The RS GGO10 O2x is best installed in a place where no air circulation occurs and to have additional insulation material on all sides. To further explain this effect imagine that the case itself only has a limited thermal coupling to the thermometer and rapid changes of the temperature will take some time before the OCXO temperature control circuit will be able to counteract. If these changes are slowed down enough the circuit is able to follow and keep the frequency within the limit where the green LED is only blinking or even stays steady green. As crystals are sensitive to changes in gravity and changes of electrical fields the unit has to be firmly mounted in a location where it doesn't get turned or shaken! Otherwise the achievable stability will suffer. In stark contrast to PLL based solutions the RS GGO10 O2x is highly immune to drops in GPS signal, missing 1PPS pulses or pulse distortions caused by fading or other influences. You can test this behavior by disconnecting the antenna for a while and the output signal will just drift with the temperature stability and aging of the oscillator. After reconnecting the GPS signal the RS GGO10 doesn't show the large swings common to PLL circuits but will move back onto locked frequency almost unnoticeable. Available Models: RS GGO10 O2P RS GGO10 O2G 1PPS input for external GPS receiver integrated GPS receiver Page 2 of 11

3 RS GGO10 O2x Specifications Frequency: Output: Phase noise (typ): 1PPS output ( O2G): Synch. 1PPS output: Power supply: GPS input ( O2G): 1PPS input ( O2P): Dimensions: Temperature range: Stability: Hold over: Aging: Interface: Soldering: Marking: Weight: 10MHz sine wave, >+4dBm into 50Ω 126 dbc/hz 10Hz offset 141 dbc/hz 100Hz offset 148 dbc/hz 1KHz offset 152 dbc/hz 10KHz offset 153 dbc/hz 100KHz offset 161 dbc typ. noise floor 3V CMOS signal from GPS RX. Normally N/C 3.3V CMOS, 1.5mA max positive pulse with 50% duty cycle. The pulse is synchronized to the average of the GPS signal. Will continue to operate with the OCXO accuracy in case of loss of GPS signal. 5VDC +/ 300mA (670mA peak) U.FL type 50 Ohm connector. 3.3V, 35mA max antenna supply. 3.3V/35mA supply for active antenna. 3.3V CMOS nominal, 3V 3.5V range 28x25.8x20.7mm (~1.1x1x0.82 ) 30 to +70C (operating) < 1x10E 10, typical <1x10E 11 (GPS locked) +/ 10ppb (free running) Stratum 3 for entire temperature range Stratum 3E if temperature after GPS loss is kept within +/ 5C compensated (GPS locked) +/ 50ppb per year (free running) after continuous operating for 30 days 3.3V 2 wire bus with address 72 or 0x48 (different addresses available for production quantities) hand or wave soldering only. Max 300C for 5 sec at the tips of the pins. RF SUISSE, RS GGO, Frequency O2G or O2P, INWAVE AG. 24g GPS receiver ( O2G model): Receiver type : 20 Channels; GPS L1 frequency, C/A Code Time To First Fix: Cold Start (Autonomous): 35s Hot Start (outdoor): 2s Hot Start (indoor): 15s Sensitivity: Tracking & Navigation: 159 dbm Cold Start (Autonomous): 144 dbm Horizontal position accuracy: Autonomous: < 10 m SBAS: < 5 m Time Pulse: 1Hz, 1µs width positive pulse, 1µs accuracy to GPS time pulse Max navigation update rate: 1Hz Operational limits: Altitude 60000ft Velocity 1000 knots Page 3 of 11

4 Required accessories: O2G: U.FL antenna cable and GPS antenna(not included) O2P: GPS receiver with 1PPS output. 1PPS has to be discontinued on failure of reception. Supply voltage: 0.5VDC, 5.5VDC 2 wire bus: 0.5 to 3.6V IND: 0.5 to 3.6V Storage temperature: 40 to +85C Output current: 1mA (for LED drive) ESD protection: 1500V human body model CAUTION: This is an ESD sensitive device! Proper ESD handling procedures have to be applied to avoid damage. Maximum Ratings I 2 C is a registered trademark of Koninklijke Philips Electronics N.V., all other trademarks are the property of their respective owners. Programming There isn't much to the programming. Everything is done via the 2 wire interface. Pull up resistors to 3.3VDC are required! (the 2 wire bus works identical to an I 2 C bus); address is 72 or 0x48. However, programming is not required for normal operation! Queries: QN QV QD QG QF read the product name (GGOxx O2), 16 bytes (xx =10 for RS GGO10 O2x) read the software revision, 16 bytes (max) read the date code, 4 bytes read the GPS jitter x10e 12, 32 bit single precision floating point little Endian read frequency error x10e 12, 32 bit single precision floating point little Endian Page 4 of 11

5 Package outline and Pinout The RS GGO10 O2x has two rows of pins with 2.54mm (100mil) spacing. Recommended hole diameter is 0.9mm RF out (1): 3.3V CMOS no decoupling capacitor inside, can directly drive 3.3V CMOS logic. 1PPS: O2P: Input for GPS 1PPS signal. CMOS 3.3V O2G: Output from GPS module, 1PPS signal. 3V CMOS (usually N/C) SDA, SCL: (IND = H or open) 3.3V 2 wire bus. (IND = L) Duo LED output (use a buffer or ultra low current LEDs!). SDA = green, SCL = red IND: H (3.3V) or open = 2 wire bus, L = Indicator LED +5V, GND: stabilized power supply, 4.5 to 5.5VDC, nominal 5VDC PPS_OUT: GPS synchronized 1PPS output, CMOS 3.3V N/C: Do NOT connect! Page 5 of 11

6 Phase noise: Typical performance data for RS GGO10 O2x Allan Variance, GPS locked (with 1 E - 9 A l a V a r 5. 2 A l l a n S T D D E V A D E V M D E V T D E V H D E V L o w e r B o u n d U p p e r B o u n d Tau = average Time ADEV = Overlapping ALLAN STD DEV. ADEV_Min = ADEV lower bound. ADEV_Max = ADEV upper bound. MDEV = Modified ALLAN STD DEV. TDEV = Time ALLAN STD DEV. HDEV = Overlapping HADAMARD STD DEV. 1 E σ ( τ ) 1 E O 1 E E τ P r o d u c e d b y A l a V a r 5. 2 A l a V a r E D a t a V a l u e s 4 E E D a t a V a l u e s 2 E E E E Page 6 of 11-2 E E - 1 1

7 5 E A l a V a r 5. 2 D a t a V a l u e s 4 E E E E D a t a V a l u e s E E E E E i n d e x E E E E E E 5 P r o d u c e d b y A l a V a r 5. 2 Allan variance of free running OCXO 1 E - 7 A l a V a r 5. 2 A l l a n S T D D E V A D E V M D E V T D E V H D E V L o w e r B o u n d U p p e r B o u n d 1 E - 8 σ ( τ ) 1 E E E E τ P r o d u c e d b y A l a V a r 5. 2 For curves demonstrating the lock, free running and re-lock performance please see our application note RF SUISSE GPS Guided References, Performance Comparison Page 7 of 11

8 Application circuits The RF out line of the RS GGO10 O2x is DC coupled. A series capacitor is recommended if not driving a 3.3V CMOS input. Caution: DO NOT DRIVE the 2 wire interface from a 5V bus! When switching from LED indicator to 2 wire mode DO NOT read on the bus within 100msec! Even though the RS GGO10 O2x has a well insulated OCXO it is highly recommended to mount it in an enclosure without airflow (i.e. from cooling fans) and add additional insulation around it (mainly top and bottom) if the best stability is desired. Moving the unit as well as vibration and electrical fields impact the accuracy too. Typical stability values of less than 1*10 11 can be achieved if these precautions are observed. Page 8 of 11

9 Triple footprint configuration for systems where an 1 OCXO, RS GGOxx O2x, RS GGOxx T2x or RS GGOxx T3x shall be implemented: For O2P model (optional solution): Page 9 of 11

10 2 Wire Programming Information The RS GGO10 series uses a standard 2 wire protocol (compatible with I 2 C ) with 7 bit addressing for communication with an external controller. The device is set by default to the address (72) decimal or 0x48 (hex). The transmission begins with a start condition on the bus followed by the 7 address bits and the R/W bit followed by an acknowledge bit generated from the addressed slave on the bus. Then the 2 wire master transmits the data bytes each followed by an acknowledge bit and a stop sequence at the end. This leads to the following bit sequence: S AAAAAAA Rw Ack DDDDDDDD Ack DDDDDDDD Ack P with: S: start condition A: address bit MSB first Rw: Read / Write bit D: Data bit MSB first Ack: Acknowledge bit P: stop condition Example Address transmission: Typical Data Transfer: The first two data bytes transmitted to the RS GGO T2G will be interpreted as a command and are shown in the datasheet as the equivalent ASCII Character. For example to query (Q) the estimated relative frequency error (F) in units of 10e 12 the following bye sequence (in hex) has to be transmitted: 0x90, 0x51, 0x46 0x90 7 Address bits plus the zero write bit > (0x48 << 1) = 0x90 0x51 ('Q') > query 0x46 ('F') > frequency error The RS GGO T2G will then calculate the response and is after 20ms available by reading the output buffer. Therefore the external controller can initiate after 20ms a read sequence on the 2 wire bus by addressing the device with the R/W bit set to 1 followed by reading the appropriate number of bytes (in this case 4 bytes) out of the buffer. Therfore the 2 wire master transmitts the following byte sequence: 0x91, 0xFF, 0xFF, 0xFF, 0xFF 0x91 7 Address bits plus the read bit set to one > ((0x48 << 1) 0x01) = 0x91 Page 10 of 11

11 0xFF, 0xFF, 0xFF, 0xFF > 4x databytes to read ( 0xFF releases the data line so the 2 wire slave has control over the data line to put the data on the bus) an INWAVE AG brand The QF command returns a 32 bit floating point number (single) in little endian format (LSByte first) in unit of 0.001ppb or relative frequency error in 10e 12. The QG command returns the estimated GPS jitter in ps as a 32 bit floating point number (single) in little endian format. QN (16 Byte), QV (16 Byte) and QD ( 4 Byte) return strings containing information about the firmware revision. Implementation Information These type of modules are usually implemented in larger systems. For these the use of a separate GPS receiver mounted close to the antenna is the better solution as the transmission of a 1PPS signal and eventually the RS232 at 4800Bd is a lot less critical than a 1.3GHz antenna cable. This also allows the customer to access the GPS information (like time or GPS status) via the interface of the GPS receiver. For this reason we strongly encourage the use of the RS GGO10 O2P for implementation into systems. All RF SUISSE product comply with RoHS requirements current at the date of delivery. As we continuously improve our product we reserve the right to change published specifications without further notice. Please see our website at suisse.ch for current information. All product manufactured and sold by INWAVE AG under the RF SUISSE brand is intended for laboratory use or are components (modules) not suitable for consumer use. Thus they are not required to and do not carry CE certification. Inquiries, quote requests and questions: please to info@rf suisse.ch or your INWAVE AG / RF SUISSE representative. For technical questions please to tech@rf suisse.ch RF SUISSE is a registered trademark of INWAVE AG, Dorf 23, CH 9411 Reute, Switzerland Page 11 of 11