Timothy Miller wrote:
On 3/17/06, Jack Carroll <[EMAIL PROTECTED]> wrote:
On Thu, Mar 16, 2006 at 09:27:40PM -0700, James Richard Tyrer wrote:
No, if you are trying to display square pixels, the rise time is important.
And displaying square pixels is _really_ important. We can't get a
fair evaluation of OGA without that.
Understood. But I think we'll have bandwidth that exceeds the 3rd
harmonic anyhow.
We are talking about the HiRes head here.
I hope that I now have this correct. The pixel rate is 500 MHz so the
maximum fundamental video frequency is 250 MHz and the 3rd harmonic is
then 750 MHz. The frequency response should be basically flat to 750 MHz.
So, if we intend to have 500 MHz dot clock frequency, the video buffer
amps do not really have enough bandwidth with a gain of 2. The ths3201
spec is 850 MHz -3dB. This could be improved by increasing the input
current of the DAC and reducing the gain of the amp.
With a current feedback amp, you can also do peaking by reducing the
value of the feedback resistor slightly.
However, it appears that the Burr Brown OPA695 would be a better choice
for a gain of 2 -- the spec is 1.4 GHz -3 dB.
We could do a better by running with a gain of 1 and differential input.
This is what is recommended for the DAC. But, this is problematic
with a current feedback amp.
--
JRT
Title: Parametric Results Download
| Part Number | Status | Number of Channels | Iq per Channel (max) (mA) | Vs (min) (V) | Vs (max) (V) | Acl, min stable gain (V/V) | BW @ Acl (MHz) | BW @ G=+2 (MHz) | GBW (typ) (MHz) | 0.1 dB BW Flatness (MHz) | Vn at Flatband (typ) (nV/rtHz) | Slew Rate (typ) (V/us) | Settling Time (0.1%) (typ) (ns) | Inverting Input Current Noise (pA/rtHz) | Noninverting Input Current Noise (pA/rtHz) | Io (typ) (mA) | Vio (max) (mV) | Offset Voltage Drift (+/-) (max) (uV/Degrees Celsius) | THD (Fc=1 MHz) (typ) (dB) | 2nd Harmonic (dBc) | 3rd Harmonic (dBc) | @ Mhz | Iib (max) (nA) | Diff Gain (%) | Diff Phase (deg) | Current Feedback | Fully Differential | Maximum Operating Supply Less Than Equal to 15V | Power Down | Video | Gain Range (dB) | Crosstalk (-dB) | Buffer | Fixed and Variable Gain | Maximum Operating Supply Greater Than 15V | Pin/Package | Approx. 1KU Price (US$) | Description |
| OPA695 | ACTIVE | 1 | 12.9 | 5 | 12 | 1 | 1700 | 1400 | | 160 | 1.8 | 2900 | 10 | 22 | 18 | 120 | 3 | 15 | -88 | 78 | 86 | 10 | 41000 | 0.04 | 0.007 | Yes | | Yes | | Yes | | | | | | 6SOT-23, 8SOIC | 1.35 | Ultra-Wideband, Current-Feedback Operational Amplifier with Disable |
| THS3202 | ACTIVE | 2 | 20 | 6.6 | 15 | 1 | 2000 | 975 | | 380 | 1.65 | 9000 | 23 | 20 | 13 | 115 | 5 | 13 | -86 | 69 | 80 | 16 | 50000 | 0.004 | 0.006 | Yes | | | | Yes | | 60 | Yes | | Yes | 8MSOP, 8MSOP-PowerPAD, 8SOIC | 2.90 | 2GHz Current Feedback Amplifier |
| THS3201 | ACTIVE | 1 | 21 | 6.6 | 15 | 1 | 1800 | 850 | | 380 | 1.65 | 10500 | 20 | 20 | 13.4 | 115 | 4 | 13 | -90 | 75 | 91 | 10 | 50000 | 0.008 | 0.007 | Yes | | | | Yes | | | | | | 5SOT-23, 8MSOP, 8MSOP-PowerPAD, 8SOIC | 2.10 | 1.8GHz Current Feedback Amplifier |
| OPA693 | ACTIVE | 1 | 14.1 | 5 | 12 | 1 | 1400 | 700 | | 200 | 1.8 | 2500 | 12 | 22 | 18 | 120 | 2 | 8 | -84 | 82 | 96 | 10 | 45000 | 0.03 | 0.01 | Yes | | Yes | | Yes | 6 | | | Yes | | 6SOT-23, 8SOIC | 1.30 | Ultra-Wideband, Fixed Gain Video Buffer Amplifier with Disable |
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