On 1/13/2015 3:17 PM, Jim Thompson wrote:
Anyone have ideas regarding how to implement a voltage-variable phase
shifter useable at 210MHz?

...Jim Thompson


I've used a variation of the normal op amp all-pass filter for this,
except with a high frequency diff amp:


*---------------*
| |
0-----*-----RRRR-------*----| |
| | | |
| R | Diff amp |
| Gain of 0.5 R | |
| R | *-----Out
| | | |
| | | |
| GND | |
| | |
*-----RRRR--*----*----| |
| | | |
| | *---------------*
| L
| L
| L
| L
L |
L |
L |
L --- Varactor
| ^
| |
| *---RRRR----0 V_phi |
| |
| CCC
| CCC big C
| |
GND GND


You pick the voltage divider to have a gain of 0.5; the series L
resonates the varactor just past the low-voltage end of V_phi;
and the shunt inductor resonates the series combination just past the
high end of V_phi. You can get about 150 degrees in one stage, with
linearity of +- a few degrees. Good medicine.

Cheers

Phil Hobbs






--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net